摘要:

Proceedinas - wof the Analytical Division ofThe Chemical SocietyCONTENTS185 Summaries of Papers185 Silver Medal Lecture193 'Medical Applications of Accelerators21 2 'Techniques for the Determination ofTrace Amounts of VolatileCompounds'21 7 'Immobilised Enzymes as Catalysts'218 Obituary-J. B. Attrill219 Equipment News221 Conferences and Meetings222 Courses222 Publications ReceivedVolume 13 No 7 Pages 185-222 July 197PADSDZ 13(7)185-222(1976)ISSN 0306-1 396July 1976PROCEEDINGSANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOF THEOfficers of the Analytical Divisionof the Chemical SocietyPresidentD. W. WilsonHon. SecretaryP. G. W. CobbHon. TreasurerJ. K. ForemanSecretaryMiss P. E. HutchinsonHon. Assistant SecretariesD. I.Coomber, O.B.E.; D. C. M. Squirrel1Editor, ProceedingsP. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington House, London, W1 V OBN.Telephone 01 -734 9864. Telex 268001.Subscriptions (non-members): The Chemical Society, Publications Sales Office, Blackhorse Road, Letch-worth, Herts., SG6 I H N .Non-members can only be supplied with Proceedings as part of a combined subscription with The Analystand Analytical Abstracts.0 The Chemical Society 1976The Analytical DivisionFourth SAC ConferenceUniversity of Birminghamwill be held a t theonJuly 17-22, 1977This Conference is organised by the Analytical Division of The Chemical Societyand sponsored by IUPAC.The scientific programme (lectures, posters, discussions and workshops) willcover all aspects of analytical chemistry; there will be an extensive exhibition ofmanufacturers' equipment and an attractive selection of social events for delegatesand their guests.Further information, including the procedure for submitting papers, is containedin the Second Circular, which will be sent shortly to all those who have alreadyrequested it. Others can obtain it by application to the Secretary of the AnalyticalDivision, The Chemical Society, Burlington House, Piccadilly, London W1 V OB

ISSN:0306-1396    

DOI:10.1039/AD97613FX023

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Vol. 13 No. 7 July 1976 of the Analytical Division of the Chemical Society Medal Lecture The following is the Silver Medal lecture delivered by Dr. J. M. Ottaway, the second SAC Silver Medallist, at an Ordinary Meeting of the Division held on October lst, 1975, and reported in the November issue of Proceedings (p. 283). Atom Formation and Interferences in Flame and Carbon Furnace Atomic Spectrometry J.M. Ottaway Department of Pure a d Applied Chemistry, UNivevsity 0-f Stvathclyde, Cathedval Street, Glasgow, G1 1XL In order to obtain results of acceptable accuracy and reproducibility by any of the atomic- spectrometric techniques, it is necessary to have a means of generating a reproducible popula- tion of atoms, which is either unaffected or affected to a known extent by the constituents of the sample matrix.Calibration with either pure standards or with standards having the same composition as the samples is then possible. In order to maintain adequate control over matrix interferences, it is useful to have some understanding of the mechanisms or causes of such interferences. In particular the matrix may interfere with the atom-formation processes or with the population of atoms in the measurement zone of an atomiser.Flame and carbon furnace atomisers have been used extensively in atomic-absorption spectrometry but while much has been written about interferences observed in flames1 much less information is currently available on furnace atomisation. Matrix interferences with the atom population will affect atomic-emission and -fluorescence measurements in the same way as atomic absorption in both types of atomisation although to date little work has been reported on emission or fluorescence from carbon furnace atomisers.In this paper, the work of the author’s research group on the study of flame and furnace atomisation and interferences is reviewed. Both practical and mechanistic studies have helped to improve our understanding and optimum use of these techniques.Flame Atomisation Fig. 1 is a schematic diagram of the processes involved in the formation of atoms in flames and is a modified version of a diagram given originally by Rubegka in Dean and Rains.1 In nearly all commercial atomic-absorption instruments, the sample solution is converted into an aerosol of fine droplets by means of pneumatic nebulisers, the efficiency of which is of the order of lo%, the residual solution being passed out of the nebuliser - mixing chamber via a drain.On entering the flame, the solvent will be evaporated from the droplets and as the temperature rises the salts formed will lose their water of hydration. It is impossible to make measurements of solid species in flames and it is possible only to predict subsequent processes but it is likely that many salts will decompose to the most-stable metal oxide at the flame temperature, although some metal halides may volatilise directly into gas molecules.Solid metal oxides can be converted into atoms by direct thermal or chemical conversion or, with a few elements, through molecular volatilisation.If the solid particle in any form is not decomposed at the temperature of the flame it may pass out through the flame in a completely undissociated form and many interferences have been ascribed to the formation of thermally stable compounds of the analyte and the interferent. The evidence for chemical reduction reactions involving solid oxides and flame radicals is not universally accepted but I believe that both chemical and thermal breakdown make a significant contribution to atom formation 186186 SILVER MEDAL LECTURE Proc.Analyt. Div. Chem. SOC. in flames. Which of these processes is more important depends on the element and the stability of its oxide and on the flame being used. Once atoms have been formed, the six species re- presented at the bottom of Fig.1 can co-exist with ground-state atoms and all can be experi- mentally observed, ground-state species by absorption techniques and excited-state species by emission. Sample so I u t ion Aerosol in a stream of and , of salt , / oxide / Molecular volati I isat ion Excited I molecules I It Excited Fig. 1 . Schematic diagram of processes occurring in flame atomisation.July, 19 76 SILVER MEDAL LECTURE 187 maximum signals in a fuel-lean air - acetylene flame whereas chromium and molybdenum give maximum atomic-absorption signals under more fuel-rich conditions.All atomic-absorption users should be aware that to obtain maximum sensitivity from their instruments the flame conditions must be carefully optimised for each element. The formation of ground-state atoms 80 - s 6 6 0 - 0 0 0 ._ +- L 2 40- c; *O I I I I 1 14.1 1 3 9 13.7 13.5 Flow meter reading Fig. 2. Variation of the atomic- absorption signal of several elements with flame composition in an air - acetylene flame at 11 mm (Perkin- Elmer 290): A, 4 pg ml-l of zinc (A, 213.8 nm); B, 25 pg ml-l of iron (A, 248.3 nm) ; C, 25 pg ml-l of cobalt (A, 240.7 nm); D, 10 pg m1k1 of chromium (A, 375.9 nm); E, 50 pg ml-l of molybdenum (A, 313.2 nm).Dotted line is for stoi- cheiometric flame composition. Acetylene to air ratio increases with decreasing flow meter reading.188 SILVER MEDAL LECTURE Froc. Analyt. Div. Chem. SOC. For example, in an interference by a metal, the (d) The nature of the accompanying ions. anions present will have an important influence on the interference.(e) The age of the sample solutions. (f) The instrument used. These effects have been demonstrated in numerous studies but two examples will be con- sidered briefly as illustrations. The interference of iron in the determination of chromium in an air - acetylene flame is affected by most of the above ~ariab1es.l~ This interference is important, for example in the determination of chromium in steel.13 It can be shown that the interference is much more serious in sulphuric or nitric acid than in hydrochloric acid (d), that the interference exists in fuel-rich conditions of an air - acetylene flame but is insignificant under fuel-lean conditions (a), and that it also varies with the concentration of iron (c).The nature of the interferent is also important with chromium, as aluminium gives an enhancement at low c~ncentrationl~ in contrast to the depression given by iron.At higher concentrations, aluminium also depresses the chromium signal14 and this interference thus changes direction with a change in concentration of the interferent. In our laboratory, we have also shown that the interference of iron, although always depressive, varies in magnitude on different instru- ments.The age of the sample solutions has not been observed to affect the determination of chromium or that of many other elements but was shown to affect interferences in the deter- mination of ruthenium.15 The methods of overcoming interferences on chromium have been reviewed elsewhere13 and we have recommended the use of an air - acetylene flame and quinolin-8-01 as a releasing agent that removes the effect of iron as iron(II1) and most other elements.Although complete release of the iron interferent by oxine was observed when using a Perkin-Elmer instrument this was not accomplished on an EEL 240 and a similar variation in performance was observed with different instruments during a collaborative study of the determination of chromium in steel by use of this method.16 When the release of interferent is incomplete, a matching concentration of iron must be added to the standard solutions if accurate results are to be obtained.Such important variations between instruments are not always taken into account and cannot be over emphasised.Interferences in the determination of calcium in air - acetylene and other flames have been described extensively,l many such interferences being ascribed to compound formation. The effects are so numerous that they present an interesting mechanistic problem. When compound formation is suspected between calcium and the interfering element or species, this should result in the depression of the atomic-absorption signals of both elements under the same conditions.In many instances, in an air - acetylene flame, in which it was possible to measure both calcium and interfering elements under the same conditions, depression of calcium atomic absorption was accompanied by an enhancement of the atomic-absorption signal of the interfering element.l0?17 In these instances compound formation appeared to be an unlikely cause of the interference.In careful and detailed studies,1° 1-mm sections of the flame were observed by placing horizontal slits on either side of the flame. All possible species of calcium were measured, including calcium atoms in ground and excited states, calcium ions (Ca+) and calcium hydroxide (CaOH) molecules in each section of the flame and under awide variation of flame compositions.Similar measurements were made in the presence of the interfering substances. Analogous measurements were also made, by emission, of flame radicals such as C,, OH and CH. It was apparent that under each flame composition, the formation of calcium atoms ceased only when the concentration of radicals reached a relatively low level.After this the atom population decayed, presumably owing t o conversion into the hydroxide, as the signal for this species began to increase under the same conditions. The appearance of calcium ions was similar to that of atoms in the hotter fuel-lean air - acetylene flame but was relatively depressed in the fuel-rich flame owing to the increased electron concentration. When an interfering element is added to the sample solution, the signals in each zone are either enhanced or depressed but the maximum calcium-atom signal occurs at the same height at each flame composition as occurs in the absence of the interferent.The correlation of atom formation and the presence of radicals suggested that flame radicals play an important role in the formation of calcium atoms and the effect of interfering substances suggested that these control the rate of formation of calcium atoms.The evidence supports a theory of atom formation by reaction of radicals at the surface of the particle formed afterJuly, 1976 SILVER MEDAL LECTURE 189 desolvation, dehydration and thermal decomposition of the salts (Fig. 1). Atoms are therefore formed by chemical breakdown of a solid particle in a solid - radical reaction, which is a surface reaction, is slow and is dependent on both the concentration of radicals in the flame and the over-all composition of the solid.The mechanism can be described schematically17 by the following CaO (solid) - where Ca represents ground-state atoms and Ca* excited-state atoms. All species are finally converted into hydroxide as air entrainment increases in the secondary diffusion zone. The observed mutual interference effects and release of interference by alkali metals can be explained by their effect on the solid - radical reaction process.17190 SILVER MEDAL LECTURE Proc.Analyt. Div. Chem. SOC. This hypothesis is supported by both thermodynamic2' and kinetic evidence28 and is a realistic mechanism for the formation of atoms in this type of atomiser where the atmosphere is essentially inert and non-reducing and the carbon tube is the only reducing agent available.In chloride medium, depressed atomic-absorption signals are commonly observed and the more volatile chloride compounds have been measured, by means of their ultraviolet - visible spectra, in the carbon tube during atomisation.In our case, molecular spectra from sodium, calcium, lead, aluminium and magnesium chloride solutions have been obtainedlg whereas with the exception of aluminium no molecular bands were obtained for the same elements in nitrate medium. One effect of chloride solutions is therefore to liberate molecular species, which may dissociate if they remain in the tube until the atmosphere has reached a sufficiently high temperature but which will probably be swept out of the tube by the non-reducing inert gas.Another interesting effect, which has been studied in some detail, is that of magnesium chloride.29 This compound completely depresses the signal of 0.1 pg ml-l of lead at a con- centration of 40 pg ml-l and seriously depresses many other elements.If, after drying the sample, the tube is heated for 30s at 1000 "C the depressive effect on many elements is removed but this is not possible with lead, which is lost if the tube is heated above 500 "C. Heating at this temperature only partially removes the effect of magnesium chloride on lead. The effect of magnesium is particularly serious in analysis of trace elements in sea water29 and clinical materials.The effect of magnesium chloride is not simply due to increased volatilisation of analyte molecules. If the analyte, e.g., lead, and magnesium are placed in different positions in the tube, the interference persists. In Fig. 3, the signal from 5 p1 of a 10 pg ml-l solution of lead placed a t the end of the carbon tube is shown to be depressed when magnesium chloride is injected a t the normal central sample position.This experiment suggests that the inter- ference occurs in the vapour phase and not in the condensed phases as, in this instance, lead and magnesium can only interact in the vapour phase. Measurement of the time dependence of the different atomic and molecular species produced from these solutions (Fig.4) shows that only the lead atoms and the molecule produced from magnesium chloride are present in the tube at the same time and capable of such interaction. The molecular ultraviolet - visible spectrum obtained on the atomisation of magnesium chloride solutions does not allow positive identification of the species involved and the use of infrared techniques is being investigated, but the decomposition of magnesium chloride is known to take place according to the following sequence30 : 118 "C MgC12.6H,0 ----3 MgC12.4H20 + 2H20 185 "C MgC12.4H,0 ---+ MgC1,.2H20 + 2H20 240 "C , MgC1,.2H20 -_MgC12.H20 + 515 "C MgC12.H20 --+ MgO + 2HC1 It therefore seems probable that the interference of magnesium chloride is at least partially caused by a vapour-phase interaction between lead and other metal atoms with HCl mole- cules that are only released above 500 "C and it is hoped to provide further evidence in support of this.July, 1976 SILVER MEDAL LECTURE 191 Time during atomisation/s Fig.3. Atomic- absorption signals for 5 pl of a 10 pg ml-1 solution of lead placed at the end of the carbon tube, A, and with 5 pl of a 1000 pg ml-I solution of magnesium as chloride placed a t the tube centre, B.Samples dried a t 100 "C before atomisation a t 2 040 "C. L I I 6 4 2 Time during atomisation/s Fig. 4. Atomic- and molecular-absorption signals observed during the atomisation of 50 p1 of a 0-1 pg ml-l solution of lead and 50 p1 of a 100 pg ml-1 solution of mag- nesium, both as chlorides : A, lead atomic-absorption signal (A, 283.3 nm) ; B, molecular-absorption signal from lead solution (A, 210 nm) ; C, molecular-absorption signal from magnesium solution (A, 210 nm); D, magnesium atomic-absorption signal (A, 285.2 nm).A and D meas- ured with hollow-cathode lamps, B and C with a deuterium arc lamp. A solution containing 100 pg ml-l of lead had to be used to obtain curve B.Solutions were dried a t 100 "C and atomised at 2 040 "C, from the centre of the carbon tube. Overlap of A and C with respect to time also occurs when thc solutions are positioned as in Fig. 3. are one to two orders lower (Table I). The wide range of elements covered in Table I and the detection power of this technique warrant further detailed study and application to real ana- lytical samples.The only application reported to date is in the determination of lithium in high-purity copper,33 which can be performed without interference from the copper matrix. TABLE I EFFECT OF TEhlPERATURE ON DETECTION LIMITS OF SEVERAL ELEMENTS BY CARBON FURNACE ATOMIC-EMISSION SPECTROMETRY Detection limitlpg ml-l rp---h----- 7 Element Wavelength/nm Normal tube Modified tube Potassium 766.49 0.000 001 6 0.000 001 9 Sodium 589.00 0.000 002 5 0.000 003 0 Lithium 670.78 0.000 07 0.000 09 Copper 327.40 0.003 6 0.002 6 Chromium 425.43 0.003 7 0.002 1 Barium 553.55 0.004 3 0.004 1 Manganese 403.08 0.007 4 0.004 4 Aluminium 396.15 0.012 0.001 0 Iron 371.99 0.016 0.010 Cobalt 345.35 0.052 0.010 Magnesium 285.21 0.094 0.001 1 Nickel 341.48 0.112 0.023 Scandium 402.04 0.14 0.014 Silver 328.07 0.16 0.014 Gold 267.60 -* 0.60 Cadmium 326.11 -* 1.6 Beryllium 234.86 - * 0.56 * Not detected a t 100 pg ml-I.Recently, the measurement of ions has been achieved during carbon furnace atomisation, using both absorption and emission techniq~es.3~ Ionisation in flames is often suppressed by the addition to the sample solution of easily ionised elements such as caesium or potassium.192 SILVER MEDAL LECTURE Proc.Analyt. Div. Chem. SOC. On such addition, the ion signal is depressed and the atom signal is increased simultane0usly.~5 When the addition of caesium was made to a barium solution during carbon furnace atomisa- tion, the ion signal was depressed but the atomic-absorption and atomic-emission signals remained unchanged.The degree of ionisation in a carbon furnace under present conditions is much lower than in flames and because of the different time and temperature dependences of atom and ion populations, ionisation interference is unlikely to be of great importance in this form of atomisation. Carbon furnace atomic-emission spectrometry offers a number of potential advantages to the analyst.Good sensitivity for a wide range of elements, freedom from matrix and ionisation interferences, much reduced spectral interferences compared to other emission sources owing to the lower excitation temperature and a small background of low noise, and low variation with wavelength are the main advantages. At present, the limitations are, firstly, that some important elements have not been observed and secondly, speed, as each determination takes approximately 3 min after dissolution of the sample, which does not compare favourably with other emission sources.Any emission technique offers the potential for simultaneous multi- element analysis and it remains to be seen if the disadvantages can be overcome by further research and development. The author thanks Professors D.W. A. Sharp and Y . G. Perkins for the facilities made avail- able at Strathclyde for this work. He is also grateful for the support and interest of many chemists in industrial and other laboratories. He is indebted to Professor E. Bishop for the original stimulation of his interest in analytical chemistry and for his consistent support and encouragement since then.The award of the SAC Silver Medal would not have been possible without the efforts and co-operation of the author’smanyresearchstudents whose contributions, whether mentioned here or not, are gratefully acknowledged. References 1. Dean, J . A., and Rains, T. C., “Flame Emission and Atomic Absorption Spectrometry,” Volume 1 , 2. Coker, D. T., and Ottaway, J .M., Natuve, Lond., 1971, 230, 156. 3. Coker, D. T., Ottaway, J. M., and Pradhan, N. K., Nature, Lond., 1971, 233, 69. 4. L’vov, B. V., “Atomic Absorption Spectrochemical Analysis,” Adam Hilger, London, 1970. 5. Coker, D. T., and Ottaway, J . M., Nature, Lond., 1970, 227, 831. 6. Coker, D. T., MSc Thesis, University of Strathclyde, 1970. 7. Rowston, W. B., MSc Thesis, University of Strathclyde, 1970.8. Davies, J. A., MSc Thesis, University of Strathclyde, 1970. 9. Pradhan, N. K., PhD Thesis, University of Strathclyde, 1972. 10. Harrison, A., MSc Thesis, University of Strathclyde, 1973. 11. Ottaway, J. M., Coker, D. T., Rowston, W. B., and Bhattarai, D. R., Analyst, 1970, 95, 567. 12. Ottaway, J. M., Coker, D. T., Davies, J . A., Harrison, A., Pradhan, N.K., and Rowston, W. U . , “Proceedings, 3rd CIS AFA,” Adam Hilger, London, 1973, p. 107. 13. Ottaway, J. M., and Pradhan, N. K., Talanta, 1973, 20, 927. 14. Ottaway, J. M., Coker, D. T., and Singleton, B., Talanta, 1972, 19, 789. 15. Hyman, M., MSc Thesis, University of Strathclyde, 1968. 16. Ottaway, J . M., “Proceedings of the 27th BSC/BISPA Chemists Conference, Scarborough, 1974,” 17.Harrison, A., and Ottaway, J. M., Proc. SOC. Analyt. Chem., 1972, 9, 205. 18. Kirkbright, G. F., Analyst, 1971, 96, 609. 19. Shaw, F., and Ottaway, J . M., to be published. 20. Shaw, F., and Ottaway, J. M., Analyst, 1974, 99, 184. 21. Shaw, F., and Ottaway, J. M., Atom. Absovption Newsl., 1974, 13, 77. 22. Campbell, W. C., and Ottaway, J . M., Talanta, 1975, 22, 401. 23. Shaw, F., and Ottaway, J. M., Analyst, 1975, 100, 217. 24. Ottaway, J . M., and Hough, D. C., Proc. Analyt. Div. Chem. SOC., 1975, 12, 319. 25. Pardhan, S. I., and Ottaway, J. M., Proc. Analyt. Div. Chem. SOC., 1975, 12, 291. 26. Pickford, C. J., and Rossi, G., Analyst, 1972, 97, 647. 27. Campbell, W. C., and Ottaway, J. M., Talanta, 1974, 21, 837. 28. Fuller, C. W., Analyst, 1974, 99, 739. 29. Campbell, W. C., PhD Thesis, University of Strathclyde, 1975. 30. Mackenzie, R. C., “Differential Thermal Analysis,” Academic Press, New York and London, 1970. 31. Ottaway, J. M., and Shaw, F., Analyst, 1975, 100, 438. 32. Ottaway, J. M., and Shaw, F., Apfil. Spectrox., submitted for publication. 33. Shaw, F., and Ottaway, J. M., Analyt. Lett., 1975, 8, 911. 34. Ottaway, J. M., and Shaw, F., Analyst, 1976, 101, 582. 35. Manning, D. C., and Capacho-Delgado, L., Analytica Chim. A d a , 1966, 36, 312. “Theory,” Marcel Dekker, New York and London, 1969. British Steel Corporation, Sheffield, 1974, p. 43.

ISSN:0306-1396    

DOI:10.1039/AD9761300185

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

July, 19 76 MEDICAL APPLICATIONS OF ACCELERATORS 193 Medical Applications of Accelerators The following are summaries of seven of the papers presented at a Meeting of the Radiochem- ical Methods Group on November 20th, 1975. Cyclotron Production of Short-lived Isotopes for Medical Use J. C. Clark 1WRC Cyclotron Unit, Hammersmith Hospital, Ducane Road, London, W12 OHS One of the principle advantages in having a cyclotron in a biomedical environment is that it enables one to consider the preparation of compounds for clinical use of the gamma-emitting radionuclides of carbon, nitrogen and oxygen.Simple compounds of carbon-11 (ti 20.3 min), nitrogen-13 (L4 10 min) and oxygen-15 (t& 2.05 min) have been used clinically for many years and still find many uses in routine diag- nosis and in research pr0cedures.l We are fortunate at Hammersmith Hospital in that not only is there a cyclotron but also we have clinical colleagues to whom the thought of working with a 2-min half-life radionuclide has advantages rather than being an impossible inconveni- ence.Some of these advantages include, for example, the in vivo visualisation of oxygen (a) 79Br(a, 2n18'Rb, half-life 4.5 h 81Rb - 81Krm, half-life 13s Target material sodium bromide. Rubidium81 recovered in one step using a small column of zirconium phosphate cation exchanger (b) 1 kg cm-' air ( C ) n H2 0 1.8% NaCl Flow 1 I min-' to face mask 0.9% NaCl solution of krypton-8l'm to perfusion catheter Flow 28 ml min-' Lead shield Mi I lipore filter Harvard Model 2206 dual syringe pump 81 Rb bound to zi rconi um phosphate Fig.1. (a) Preparation of krypton-8lm; ( b ) recovery of krypton-8lm in the gas phase for ventilation studies; and c ) recovery of krypton-8lm solution for perfusion studies. utilisation (not possible by any other technique) and the possibility of making sequential measurements at low radiation dose to the patient without background interference from the previous measurement.Furthermore, if the half-life of the administered radionuclide is of the order of a few seconds, one can envisage the situation like an X-ray technique where the radionuclide is present in the subject only during the measurement. The use of krypton-81m with its half-life of 13 s is an example of this approach. The use of a radionuclide generator loaded with rubidium41 (ti 4.5 h) makes it possible to carry out investigations with krypton-81m even at sites remote from the cyclotron.2194 MEDICAL APPLICATIONS OF ACCELERATORS Proc.Analyt. Div. Chern. SOC. The method of preparation and modes of operation of krypton-81m generators are outlined in Fig. 1. TABLE I REACTIONS USED TO PROVIDE OXYGEN-15 AND NITROGEN-13 LABELLED COMPOUNDS FOR CLINICAL APPLICATIONS Oxygen-15 (ti = 2.1 min) 14N(d, n)l5O I I I 1 N, - CO, (95 + 5)l Gas target N, - 0, filled with: (96 + 4)l ~ 1 5 0 , I 150, I (150 "C) ~ ~ 1 5 0 c150 Nitrogen-13 (th = 10 min) 12C(d, n)l3N Deuteron irradiation of CO, results largely in the production of l3N,.lI3 Deuteron irradiation of CH, results in the production of 13NH, together with a variety of 13N-labelled amines.* Proton irradiation of 0, at high pressure and temperature results in a mixture of nitrogen oxides.5 Proton irradiation of H,O results in 13N0,- and 13N0,- mixture, readily reduced with titanium- (111) chloride t o high-purity, high specific activity 13NH,.6 l3NH3 has uses in in vivo studies of heart function and has also been used in the enzymatic syntheses of several 13N-labelled bio-organic compounds.' JL f- > 160(p, u)13N Table I shows some reactions that have been used to provide oxygen-15 labelled compounds The production of nitrogen-13 labelled nitrogen has been carried More recently, the preparation of 13N0, Ammonia has found uses as 13NH,+ and as substrate in the The development of the use of An outline of the production methods for several Examples of the type of reactions that have for clinical applications.out for many years for pulmonary investigations. and 13NH, has been described. enzymatic synthesis of nitrogen-13 labelled compounds. carbon-11 has followed a similar pattern. simple chemical forms is shown in Table 11. TABLE I1 EXAMPLES OF METHODS USED FOR THE PRODUCTION OF CARBON-11 AND FLUORINE-18 Carbon-11 (it = 20.3 min) h 7 > llB(d, 2n)llC B,O, target material, irradiations 1°B(d, n ) W yield llC0 or 11C02 if carried out llB(p, n ) X under H, or He, respectively.s X O , directly.When N, + 5% 14N(p, cc)llC N, usual target material yields H, is irradiated, target effluent contains 11CH4 + radiolytically produced NH,. When this mix- ture is passed over heated Pt, HllCN is produced.9 1 Fluorine-18 ( t g = 110 min) h r 7 1 6 0 ( ~ , pn)lsF '1 Generally H,O targets, yielding 160 (We, n) lSF J F- (as.). lo *l1 ,*Ne(d, u)lSF Neon gas targetry lends itself t o anhydrous procedures more appro- priate t o fluorine synthetic chem- istry, e.g., NO18F, lSF,, AglsF, AglsF,, SblsF5 and ArN2B18F4 (Schieman reaction for Ar18F) .12 been used to incorporate carbon-11 as I1C0, into organic compounds are shown in Fig. 2.Fluorine-18, with its 110-min half-life, has also received some attention as a potential label for organic compounds.July, 1976 MEDICAL APPLICATIONS OF ACCELERATORS 195 /o HI R-C( ”CH3OH ____c ”CH31 LiAlH{ Fe - Mo 1 375 OC catalyst R’ CH~OH R’ COOH (refs. 15,16) (ref. 15) H’ CHO RNH;! NaBH4 Paraquat’* I R-NfiCH3 H (applicable to proteins) ’ 3,14 Fig.2 . Some synthetic routes that have been used to incorporate carbon-11 into organic compounds. References 1. Clark, J. C., and Buckingharn, P. D., “Short-lived Radioactive Gases for Clinical Use,” Butterworths, 2. Clark, J . C., Watson, T . A,, and Horlock, P. L., Radiochevn. Radioanalyt. Lett., 1976, in the press. 3. Welch, M.J., Chem. Commun., 1968, 1354. 4. Tilbury, R. S., Dahl, J. R., and Laughlin, J. S., Radiochem. Radioanalyt. Lett., 1971, 8, 317. 5. Parks, N. J., Peek, N. F., and Goldstein, E., I n t . J . Appl. Radiat. Isotopes, 1975, 26, 683. 6. Krizek, H., Lembares, N., Dinwoodie, R., Gloria, I., Lathrop, K. A., and Harper, P. V., J . Nucl. M e d . , 7. Cohen, M. B., Spolter, L., MacDonald, N.S., Masuoka, D. T., Laws, S., Neely, H. H., and Takahashi, J., 8. Clark, J . C., and Buckingham, P. D., Radiochem. Radioanalyt. Lett., 1971, 6, 281. 9. Christman, D. R., Finn, R. D., Karlstrom, K. I., and Wolf, A. P., Int. J . Appl. Radiat. Isotopes, 1975, 10. Clark, J. C., and Silvester, D. J., I n t . J . Appl. Radiat. Isotopes, 1966, 17, 151. 11. Tilbury, R. S., Dahl, R., Mamacos, J.P., and Laughlin, J. S., I n t . J . Appl. Radiat. Isotopes, 1970, 21, 12. Palmer, A. J., Clark, J . C., and Goulding, R. W., Int. J . A$@. Radiat. Isotopes, 1976, in the press. 13. Marche, P., Marazano, C., Maziere, M., Morgat, J. L., de la Losa, P., Comar, D., and Fromagot, P., 14. Straatmann, M. G., and Welch, M. J., J . Nucl. Med., 1975, 16, 425. 15. DeGrazia, J .A., Rodden, A. F., Teresi, J. D., Busick, D. D., and Walz, D. R., J . Nucl. Med., 1975, 16. Robinson, G. D., and MacDonald, N. S., J . Nucl. Med., 1973, 14, 446. 17. Lifton, J . F., and Welch, M. J., Radiat. Res., 1971, 45, 35. 18. Palmer, A. J., unpublished work. London, 1975. 1973, 14, 629. in “Radiopharmaceuticals and Labelled Compounds,” IAEA, Vienna, 1973, p. 483. 26, 435.277. Radiochem. Kadioanalyt. Lett., 1975, 21, 53. 16, 73. Distribution of Lead in Teeth J. H. Fremlin and W. Tanti-Wipawin Department of Physics, University of Birmingham, P.O. Box 363, Birmingham, B15 2TT There is currently much concern with the amount of lead in our environment. This lead is derived from petrol and from a variety of industrial activities and is at such a level that the concentration of lead in the blood of city children is often within a factor of three of the level at196 MEDICAL APPLICATIONS OF ACCELERATORS PYOC.AnaZyt. Div. Chem. SOC. which clinical symptoms would be expected, and may already be producing undesirable effects on brain development. Measurement of lead in the teeth is being used to give information on the integrated uptake of lead by the individual concerned over a period, while blood measurements may show only very short-term values of less importance. We have been examining the distribution of lead within individual teeth, with the object of distinguishing lead deposited during formation or calcification of the tooth from that taken up by the tooth over its working life after eruption.It is then bombarded with 30-MeV ions of helium-3 from the Birmingham 1.52-m cyclotron, which produces polonium isotopes by reactions mainly of the types Pb(3He, 3n)Po and Pb(3He, 4n)Po.As there are four stable lead isotopes, a range of polonium isotopes is produced, but several of these are very long lived and of little use; the main useful activity is due to polonium-206, which has a half-life of 8 d and emits a-particles.These particles can be recorded by a plastic solid-state track detector without interference from the large number of p- and y-activities produced in the other elements present. The main problem in the bombardment is to remove the heat delivered by the highly energetic helium-3 ions. These ions will penetrate 0.5 mm into dental tissue but the a-particles from the polonium-206 have a range of only about 20 pm.It is therefore advantageous to bombard the tooth at a shallow angle to the surface so that the effective part of the helium-3 track lies close to this surface. We also mount 20-40 tooth sections at a time on a rotating target, as shown in Fig. 1, each pair of sections being cemented on to a removable aluminium plate. A tooth is sectioned along a suitable plane and the cut section is polished. Fig.1. Photograph of the rotating target used for simultaneous irradia- tions of tooth sections. This arrangement enables us both to run the cyclotron fairly efficiently with an external beam current of 2.5 p A (corresponding to a power of 75 W) and to keep the heating of each tooth surface within acceptable limits.On one of the plates is cemented a section of glass with a known lead content as a standard. The bombardment takes place outside the cyclotron vacuum, the beam being brought through a thin Havar window so that the target can be cooled by an air blast during bombardment. For satisfactory yields of polonium-206 from lead at a concentration of 1 p.p.m. a bombardment of 1 p A h cm-2 is sufficient, but to avoid damage to the tooth surface this bombardment may take several hours to deliver.After allowing the short-lived activities of the target to cool for safe handling, each alum- inium plate with its tooth section or standard glass sample is placed in contact with a thin sheet of cellulose nitrate (LR 115 type 2), close contact being maintained with the help of aJuly, 1976 MEDICAL APPLICATIONS OF ACCELERATORS 197 pressure pad.The outline of each tooth section is marked on the plastic backing and the latter is then etched for 2.5 h in a 25% solution of sodium hydroxide at 55 "C. a-Particles passing into the plastic leave damage trails up to 20-30 pm long containing large numbers of broken chains and free radicals.Such a track is etched out much more rapidly than is the undamaged surface and the initially very small diameter is then etched out to 1-2 pm, when it can easily be seen under the microscope. The number of tracks per unit area is then proportional to the lead content in the region of tooth with which this area was in contact. The position of the track on the plastic can be recorded to a few micrometres but the point of origin of the a-particle may be several micrometres down in the tooth and it may not emerge normally so that the definition of the position of the original lead is not better than about 20 pm.Fig. 3 shows a smaller scale photomicrograph of a complete tooth section. The larger concentration in the cementum that covers the root of the tooth, and in the dentine around the pulp cavity, can be clearly seen.Smaller concentrations on worn areas of the biting surfaces of the enamel can also be seen. These are evidently the result of lead take-up after eruption of the tooth: whereas the lower concentration over the general area of dentine and enamel is due to lead laid down during the original formation of the tooth.All samples are left for about 4 weeks. A photomicrograph of a typical set of tracks is shown in Fig. 2. Fig. 2. Photomicrograph of CI- particle tracks in cellulose nitrate film. Fig. 3. Photomicrograph of the distribution of a-particle tracks from a complete tooth section, showing the high concentrations of lead in the pul- pal dentine, the cementum and worn parts of the enamel surface.The absolute concentrations of lead corresponding to the track densities observed are obtained by comparison with the number of tracks per unit area derived from the reference lead glass irradiated at the same time. A glass standard is used because the density of glass, and hence the range of a-particles, are close to those of the dental tissues. At the levels of lead normally observed, however, small errors here are not of great importance. It can be seen from Fig.3 that the statistical errors will be several per cent. even of averages over fairly large areas of the tooth. Such errors could be reduced by longer bombardments but the normal biological variations between individuals, or even between different teeth of the same individual, are usually much greater than the errors observed so that this is not necessary in the present instance.We are grateful to Mr. E. E. Cartwright and Mr. F. R. Stewart for technical advice and for carrying out the bombardments, to Mr. J. A. Dennis for the skilful construction of the target itself and Mr. J. E. James for the photograph in Fig. 1.198 MEDICAL APPLICATIONS OF ACCELERATORS Proc. Analyt.Div. Chem. SOC. Measurement of Lead and Other Elements in Biological Material by Proton- induced X-rays N. A. Dyson and A. E. Simpson Depavtment of Physics, Univevsity of Birmingham, P.O. Box 363, Birmiizghant, B15 2TT When matter is bombarded by protons, inner-shell ionisation of the atoms occurs and character- istic X-rays are emitted. The intensity depends on the cross-section for inner-shell ionisation, the fluorescence yield of the emitting atoms and the thickness of the target.The ionisation cross-section depends upon the proton energy in relation to the shell binding energy. There is no critical excitation energy, in contrast to the situation when an electron beam is used, and the form of the variation of cross-section with bombarding energy is also different.Several studies of X-ray production by proton bombardment have been reported (e.g., refs. 1-3). We have studied the variation of X-ray intensity with proton energy, for targets thick enough to bring the protons completely to rest, using protons with an incident energy between 200 keV and 3 MeV. An important parameter is the ratio of proton velocity to the “Bohr orbital velocity’’ of the electrons in the shell in question.When this ratio is much less than 1, the yield of characteristic K X-rays has been found experimentally to vary approxi- mately as the sixth power of proton energy, and there is also some theoretical justification for this, following the theory of Merzbacher and L e ~ i s . ~ , ~ At higher proton energies, the varia- tion of yield with energy is less strong, partly due to a less steep rise of inner-shell ionisation cross-section, and partly due to the increasing self-absorption of the X-rays being produced a t progressively greater depths within the target.The yield is found to fall very rapidly with increasing atomic number ( Z ) , and a 2-12 depen- dence has been predicted by Merzbacher and Lewis.For high-2 elements such as lead, the yield of K X-rays is unobservably low at the proton energies investigated by us, but the L spectrum is excited strongly. The L spectrum varies with proton energy in a manner some- what similar to the K radiation, and Fig. 1 illustrates the yield (expressed as photons per proton, emitted in 47r steradians) from tungsten in the range 0.2-0.5 MeV, and from lead in the range 0.5-3 MeV.The spectrum obtained from pure lead at 2.5 MeV, using the apparatus described below, is illustrated in Fig. 2. This spectrum is, however, very much weaker than the continuum produced by electron bombard- ment, mainly because the changes of velocity and direction experienced by the protons passing through the coulomb field of the target nuclei are very much less than would be experienced by electrons, because of the greater mass of the proton.There are other mechanisms that contribute to the background (some of which are referred to briefly below), but the fact remains that the characteristic radiation from proton bombardment is very pure, giving very high peak-to-background ratios, whereas in electron bombardment the intensity of the continuum is substantial and often accounts for the greater portion of the emitted radiation intensity, especially when targets of high atomic number are used.It is this fact which makes proton bombardment attractive for the measurement of concentrations that are considerably below the detection limit of, for example, the electron microprobe. We have been using proton-induced X-rays for the study of lead, zinc and copper in material of biological origin, mainly human blood and liver tissue. If the targets are thick (in the sense defined above), and if the concentration of the element is low, the counting rate under a peak is proportional to the concentration of the element giving rise to that peak, and this concentration can therefore be determined by comparison with suitable standards.The standards have usually been materials of relatively low atomic number to which small known amounts of the element under investigation have been added. In this way, corrections for stopping power and for partial absorption of the emergent X-rays can be avoided. The proton beam has been provided by the Dynamitron accelerator in the Birmingham Radiation Centre, which gives a beam of well defined energy in the range 1-3 MeV.We have used a stainless-steel target chamber of simple T-piece design, in which the proton beam strikes the target at 45” to the target surface, the emitted X-rays being viewed at 90” to the proton beam. The diameter of the beam is defined by a 3-mm circular aperture, giving an elliptical “spot size” of about 10 mm2 on the target surface.Although the emitted X-rays pass through In addition to the characteristic X-rays, a continuous X-ray spectrum is produced.July, 1976 MEDICAL APPLICATIONS OF ACCELERATORS 199 a series of windows of low-2 material before being detected by the lithium-drifted silicon detector, they do not constrict the field of view defined by the crystal diameter (1 cm); furthermore, the X-ray absorption introduced by them is not significant at the energies of interest (5-20 keV).The whole T-piece is electrically insulated from the apertures and the remainder of the beam line, and is in good electrical contact with the target, thus facilitating collection of most of the secondary electrons emitted by the target.This allows for accurate measurement of the the proton current striking the target. 0.3 0.4 0.5 0.6 0.70.80.91.0 1.5 2.0 E, /MeV 1 ~- 8 10 12 14 16 Photon energy/keV Fig. 2. L X-ray spectrum from pure lead ( E p = 2.5 MeV). Fig. 1. Variation of L X-ray yield from (A) tung- Broken lines: Lt,t. cc Ep6. sten and (B) lead. In all instances, except for metals (which were in the form of self-supporting foils), the specimens were mounted on to ultrapure aluminium foil; the Kcc radiation of aluminium (at 1.49 keV) lies outside the region of interest, the fluorescence yield is low (0.038) and the radiation is strongly absorbed by the windows and air-path, so that the backing foil does not provide a source of interference with the X-rays from the specimen.An aluminium cover- slip of the same high purity, and with a central circular aperture, was placed over each specimen to keep it in good thermal and electrical contact with the target holder. The target so prepared was clamped by means of an aluminium frame on to the copper “finger” that extends into the proton beam. Liquid specimens were evaporated directly on to aluminium backing foil, drop by drop, over a warm hot-plate and, with solid tissue, a section from the specimen was directly clamped between the backing foil and cover-slip.In both instances, the targets were then completely dried in a vacuum desiccator. We have carried out an analysis of human blood, and the results for five elements are shown in Table I. It can be seen that, with the possible exception of lead, the results are broadly consistent with existing published data, bearing in mind the wide range of concentrations tabulated by Kubota et aL6 The sensitivity of the method depends on the statistical fluctuations of the counts recorded in a characteristic X-ray peak, and the fluctuations in the background continuum that is measured on each side of the peak.Our earlier studies using 450-keV protons from a Cockroft - Walton accelerator showed that nickel and neighbouring elements should be detectable in evaporated inorganic salts down to concentrations in the region of 8 p.p.m.Even with this200 MEDICAL APPLICATIONS OF ACCELERATORS Proc. Analyt. Div. Chem. SOC. relatively low proton energy, trace elements can thus be detected at low concentrations in biological material.More recently, using the Dynamitron, we found that the detection limit is progressively lowered (improved) as the proton energy is raised. Using samples of blood to which small concentrations of zinc and lead had been added, analysis of the data has shown that concentraions down to 0.7 and 2 p.p.m., respectively, in solid organic material should be detectable, corresponding to concentrations of 0.1 and 0.3 ,ug ml-l in whole (“wet”) blood.TABLE I MULTI-ELEMENT ANALYSIS OF WHOLE HUMAN BLOOD E, = 1.50 MeV. All concentrations in micrograms per millilitre of whole blood. Kubota et a1.6 This work W L - Element (p, X) Bowen’ Mean Range Pb 0.8 0.27 0.14 0.07-0.20 cu 0.8 1.07 0.89 0.57-1.74 Zn 2.7 6.5 5.3 1.98-10.08 Fe 227 475 Br 2.3 4.6 - - - - The result for lead in Table 1 is therefore rather near the limit of detection, and it was therefore of interest to compare it with data obtained by X-ray fluorescence analysis using a Philips 1410 X-ray fluorescence spectrometer (in the Centre for Materials Science).The comparison is shown in Table 11. Very good agreement exists between the two measure- ments. It is interesting to note that in spite of the greater energy resolution of the crystal spectrometer used in the X-ray fluorescence analysis, the (p, X) analysis achieved a lower statistical error and used a much smaller sample (a few drops as opposed to several millilitres).TABLE I1 ANALYSIS FOR LEAD OF A SAMPLE OF WHOLE HUMAN BLOOD (PLUS ANTI-CLOTTING AGENTS) Method Leadlpug ml-l Proton-induced X-rays (E, = 1.50 MeV) 0.86 (& 0.21) X-ray fluorescence 0.83 (& 0.30) A typical proton-induced X-ray emission spectrum for blood is illustratedin Fig.3. Analysis of the data shows that the lead La radiation is statistically significant, with the standard deviation given in Table 11. The study of liver tissue is of interest in connection with certain metabolic diseases in which the trace-element balance is changed, for example, liver cirrhosis. In this instance, the copper balance is changed, leading to greatly increased deposition of copper in the liver.We have examined sections of normal liver, obtained at autopsy, and have analysed it for a number of elements, particularly copper and zinc. Quantitative analysis was carried out by proton- induced X-ray emission analysis using the calibration standards of blood referred to earlier, and correcting for the differing water contents of blood and liver. Our mean values for copper and zinc in normal liver were 8.1 and 54.5 p.p.m., respectively, which may be compared with values of 8.6 and 46 p.p.m.tabulated in reference 8. We have also analysed liver sections obtained a t autopsy from a patient who had suffered from primary biliary cirrhosis.Our mean value for copper was 484 4 60 p.p.m., an increase by a factor of 60, and our value for zinc was 217 & 28 p.p.m., an increase by a factor of 4. Clearly these elevated values can be measured readily by this technique and, because only very small samples of material are needed, the technique would appear to be suitable for multi-element analysis of needle biopsy specimens.Although the sensitivity improves gradually with increasing proton energy, as noted above, the improvement between 2.5 and 3 MeV is small, and it seems that a further increase in proton energy would not be beneficial. The background (continuum) radiation is expected to increase more rapidly as the proton energy increases beyond this value, and there are at least two reasons for this effect : firstly, nuclear reactions and the gamma radiation associated withJu,ly, 1976 MEDICAL APPLICATIONS OF ACCELERATORS 201 them become increasingly important ; secondly, the continuous X-ray spectrum (bremsstrah- lung) produced by “knocked-on” electrons increases in intensity and in photon energy.The maximum kinetic energy of these electrons may readily be shown to be given by (4m/M)E,, where m and M are the masses of electron and proton, respectively, and E , is the proton energy. For 2-MeV protons, the knocked-on electrons have maximum energies of about 4.5 keV and so will not contribute to the energy region of interest in the above analyses, but with, e g ., 4-MeV protons, this will increase to about 9 keV, and the bremsstrahlung produced by them will consequently begin to encroach into the energy region occupied by the character- istic radiation of copper and zinc, tending to reduce the sensitivity for these elements. For 1 ., Iron -. 4 6 Copper - \ .. . I . Zinc a . 1 . Iron 1 :9 8 10 12 14 Photon energylkev Fig. 3.X-ray spectrum from blood. ’chin targets, the knocked-on electrons will leave the target in the forward direction with little opportunity for emitting bremsstrahlung, which may enable somewhat higher proton energies to be used with advantage. This “thin-target” technique has not been explored by us, because it leads most directly to a determination of mass rather than concentration; discussions of these aspects have been given by, e.g., Johansson et aL9 In conclusion, simultaneous analysis of several elements is possible, leading directly to the determination of concentrations down to levels of the order of 1 p.p.m.Further, this deter- mination can be carried out using relatively simple methods of specimen preparation. No chemical separation procedures are necessary, and only a few milligrams of material are required.For these reasons, this method of analysis promises to be of increasing interest In the fields of medicine and biology. References 1. Messelt, S., Nzicl. Phys., 1958, 5 , 435. 2. Shima, K., Makino, I., and Sakisaka, M., J . Phys. SOC. Japan, 1971, 30, 611. 3. Duggan, J. L., Beck. W. L., Albrecht, L., Munz, L., and Spaulding, J. D., Adv.X-ray Analysis, 1972, 4. Merzbacher, E., and Lewis, H. W., in Fliigge, S., Editov, “Encyclopaedia of Physics,” Volume 34, Springer- 5. Dyson, N. A., J. Phys., B, 1973, 6, 562. 6. Kubota, J., Lazar, A., and Lossee, G., Lfrchs Enviv. Hlth, 1968, 16, 788. 7. Bowen, H. J. M., “Trace Elements in Biochemistry,” Academic Press, New York, 1966. 8. International Commission on Radiological Protection, Report of Committee I1 on Permissible Dose for 9.Johansson, T. B., Akselsson, R., and Johansson, S.E.A., NucZ. Instrum. Meth., 1970, 84, 141. 15, 407. Verlag, Berlin, 1958, p. 166. Internal Radiation, 1959.202 MEDICAL APPLICATIONS OF ACCELERATORS Proc. Analyt. Div. Cheun. soc. Determination of Copper and Zinc in Bone Ash Using Accelerator- Produced y-Photons D.R. Williams and J. S. Hislop Environmental and Medical Sciences Division, AERE, Harwell, Didcot, Oxfovdshive, OX1 1 ORA Prior to a survey of the concentrations of ccpper and zinc present in human bone, a homo- geneous intercomparison material, consisting of ashed animal bone meal, was prepared in order to assess the relative capabilities of several different analytical techniques for this analysis. Of particular interest was the use of high-energy y-photon activation, which, until recently,1,2 has mainly been used for the determination of the light elements oxygen, carbon, nitrogen and fluorine.It has, however, a number of favourable features for the determination of other elements, particularly in biological materials, e.g., it does not suffer from errors due to apparatus or reagent blank, and, compared with thermal neutron activation, a different range of isotopes is produced, which (a) enables additional elements, such as lead and nickel, to be determined much more easily and (b) does not give rise to high levels of matrix activities, such as phosphorus-30 and sodium-24.Choice and Production of Radionulides Irradiation of copper and zinc with high-energy y-photons induces reactions of the type (y,n) etc., The nuclides on which this work is based are shown in Table I, although other reactions, e.g., 66Zn(y,11)~~Zn, are also of analytical value.These isotopes have suitable nuclear properties to permit the determination of their parent elements using the 511-keV annihilation radiation of copper-64 and the 184.6-keV y-ray of copper-67. The attraction of the y-activation technique is that a single radiochemical separation of copper from the bone matrix allows the simultaneous determination of both copper and zinc.However, as copper-64 is also produced from zinc, the copper concentrations must be corrected for zinc interference. It can be seen that both copper and zinc give rise to isotopes of copper.Experimental Irradiation is carried out in bremsstrahlung produced by dissipating about 10 pA of 45-MeV electrons in a 3 mm thick tungsten converter using the Harwell 45-MeV electron linear acce1erator.l Up to four 1-g samples of bone ash, together with thin foils of pure copper and zinc, are irradiated for 1 h. After a decay period of 1 h, copper is radiochemically separated from the samples using the procedure outlined in the scheme below.The over-all chemical yield is approximately 60%. Dissolve in presence Make 0.1 N (HCl) of Cu (+ K, Sr)- + and extract with ditliizone in CHCI, .1 Precipitate CuSt- Back-extract Cu from 2 N HC1 with 10 N HCl I I .1 --f Reduce CuII to CuI, Dissolve in HNO, Fe (OH) , scavenge precipitate as CuSCN Copper thiocyanate is precipitated directly from aliquots of reduced acidic solutions of (a) the copper standards and (b) the zinc standards dissolved in the presence of a known amount of copper.The activities of copper-64 and copper-67 are measured using a 3-in NaI(T1) detectorJuljy, 1976 MEDICAL APPLICATIONS OF ACCELERATORS TABLE I 203 NUCLIDES USED TO MEASURE COPPER AND ZINC IN BONE ASH Production Product Half- Threshold for process nuclide life/h y-Rays production/MeV 65Cu(y, n) 64Cu 12.8 /3+511 9.9 6 8 w Y 9 P) 67Cu 58.3 185 17.7 'OZn(y, t) 67Cu 58.3 185 17.2 Ixtevfevences 66Zn(y, np) 64Cu 12.8 p++511 18.8 64Zn(n, p) 64Cu 12.8 p+--+511 18.8 in conjunction with a multi-channel analyser.Repetitive activity measurements are made on samples and standards to confirm the purity of the 511- and 184.6-keV photopeaks.The correction for copper-64 formed from zinc is obtained by measuring the 511-keV activity of the sources prepared from the zinc standards. This shows that each 1 pg of zinc produces an apparent 0.025 pg of copper. Results The results obtained for bone ash are given in Table 11. In addition, to assess the applic- ability of the method to other types of biological material, the results from a restricted number of analyses of NBS Standard Reference Materials are also included.TABLE I1 COPPER AND ZINC IN BONE ASH AND STANDARD REFERENCE MATERIALS Element Copper Zinc Mean and illaterial Method coefficient of variation Bone ash Emission spectrometry 15 Bone ash Colorimetry 12.5 2.5 Bone ash Neutron activation 11.5 f 0.4 Bone ash Photon activation 11.2 & 2.2 NBS 1591 Photon activation 12.1 i_ 1.37 NBS 1577 Photon activation 183 f S l Bone ash Emission spectrometry 230 Bone ash Colorimetry 233 -& 5 Bone ash Neutron activation 228 f 5: Bone ash Photon activation 210 f 16 NBS 1591 Photon activation 29.3 & 2.57 NBS 1577 Photon activation 150 f lot (orchard leaves) (bovine liver) N" 3 16 5 4 1 1 3 12 2 10 1 1 Certificate value - - - - 12 f 3 193 & 10 - - - - (28) 130 f 10 * N = number of determinations.t Errors based solely on l o counting statistics. Estimated over-all error &lo% (lo). $ Mean and range. For copper, the agreement with independent techniques is within the reported standard deviation and the precision, although not as good as that of thermal neutron activation, is comparable to that of the more conventional methods. For zinc, again the agreement is satisfactory but the precision is poorer than that of the other methods.Assuming average induced activities, decay times, chemical yields and counting times, the limits of detection for copper and zinc are 0.1 and 1.0 pg, respectively.Conclusions Activation analysis using high-energy y-photons has been shown to be applicable to the determination of copper and zinc in bone ash and Standard Reference Materials. This confirms that the method is suitable for the determination of heavy elements in certain bio- logical materials and is of value as an independent technique in assessing the accuracy of more204 MEDICAL APPLICATIONS OF ACCELERATORS R o c . Analyt.Div. Chem. SOC. conventional procedures although, in terms of absolute sensitivity, it :cannot compete with thermal neutron activation, especially for copper. References 1. Hislop, J. S., and Williams, D. R., Rep. U.K. Atom. Energy Auth., AERE-R-6910, 1971. 2. Hislop, J. S., and Williams, D. R., J . Hadioanalyt. Chem., 1973, 16, 329.3. Anderson, P., Hislop, J. S., and Williams, D. R., Rep. U.K. Atom. Energy Auth., AERE-R-7823, 1974. Activation Analysis /n Vivo of the Human Body Using Cyclotron- produced Neutrons T. J. Spinks and D. K. Bewley iWRC Cyclotvon Unit, Hammersmith Hospital, Ducane Road, London, W12 OHS 1% vivo neutron-activation analysis, using the Medical Research Council cyclotron at Hammer- smith Hospital, is being carried out in an attempt to assess the body content of certain ele- ments.The patients being studied are suffering from various diseases that affect the skeleton and our principle interest is in changes in calcium content with treatment. Whole- body Activation Irradiation of the body with a fast neutron beam induces amounts of calcium-49, sodium-24 and chlorine-38 by thermal neutron capture and aluminium-28 and nitrogen-13 by fast neutron reaction on phosphorus and nitrogen.Smaller amounts of other isotopes are produced but are not of great significance in our studies. In all centres that have used ~ Y Z vivo activation, interest has been focused on calcium because it is nearly all contained in the skeleton and thus occupies a clearly defined site in the body.Total-body calcium ought then to be a good index of total skeletal mass. Phosphorus is mostly contained in the skeleton but about 1004 is in soft tissue while sodium, chlorine and nitrogen are more evenly distributed. Neutron activa- tion is unable to discriminate between soft tissue and bone. I n order to obtain an adequate assessment of body calcium, one must ensure that each gram of element is activated to the same extent. This is, in practice, impossible as the body presents a structure of non-uniform thickness to an incident neutron beam and each person, further- more, has a unique shape.There is a particular problem with activation of the skeleton which is itself of a very irregular geometry. The reaction that makes analysis of calcium possible is the capture of thermal neutrons by naturally occurring calcium-48 to form calcium-49.This nuclide emits y-rays, mainly of energy 3.1 MeV, which suffer only small interference from the y-rays emitted by the other products of activation. Interference is due to slight spectral overlap from the 2.75-MeV line of sodium-24 and the production of a small amount of sulphur-37 from (n,p) reaction on chlorine-37.Sulphur-37 also emits a y-ray of energy 3.1 MeV. In our work, the total count rate due to these interferences is about 4% of that from calcium-49. In order to obtain an adequate uniformity of thermal neutron flux throughout the body, the patient is surrounded with sheets of polythene 5.5 cm thick to partially thermalise the neut- rons, and irradiated bilaterally.The mean incident neutron energy is 7.5 MeV with a maxi- mum of about 18 MeV.1 The neutrons are produced by bombarding a beryllium target with deuterons of energy 16 MeV. The patient is positioned as far as possible (about 4 m) from the target and the incident fast flux is uniform over the patient to within *5%. By placing gold foils a t various points within a water-filled man-like phantom, it was found that the thermal flux varied by *l2yb from the mean.The total irradiation time is about 20 s; 0.05 rad is delivered anteriorly in 10 s, the patient is then turned by remote control through 180" in 12 s and a further dose of 0.05 rad is given posteriorly. The dose is monitored by an ionisation chamber (air filled) near the beryllium target and by the activity of a bottle of sodium nitrate solution placed next to the patient, After irradiation, the patient is transferred in about 3 min to a steel-walled (15 cm thick) whole-body counter containing ten NaI(T1) detectors (15 cm hameter x 10 cm thick).TwoJdj.~, 1976 MEDICAL APPLICATIONS OF ACCELERATORS 205 standard stationary geometries are used, one for patients under and one for those over 165 cm tall, designated LG and SG, respectively.The detectors are positioned so as to view the patient’s body as uniformly as possible and are placed about 20 cm from the body surface. The standard deviation of the calcium-49 count rate for six repeat activations of a cadaver under the same conditions was a%, the same as the statistical deviation.The main types of metabolic abnormality being studied are Paget’s disease, hyperpara- thyroidism, osteoporosis and Cushing’s disease. In the first two, serum calcium increases as a result of over-production of parathyroid hormone, and leads to softening and rarefaction of bone. Paget’s disease is characterised by local increases in bone resorption and formation, which produce severe pain and deformity.Osteoporosis is a condition in which skeletal mass decreases below the level needed for proper support, one of the early signs of which is vertebral crush fractures. Cushing’s disease, caused by over-production of glucocorticoids by the adrenal cortex or by a basophil tumour of the pituitary, is characterised in some cases by osteoporosis.The procedure we follow is to compare the calcium-49 count rate per unit of neutron dose received with the initial determination of this quantity for each patient (usually before treat- ment is begun). Provided that the patient’s body build, which affects neutron and y-ray scattering, has not changed significantly over the period of observation, such comparisons are valid. The detection of changes in total-body calcium is obviously not, in itself, diagnostic and must be related to other parameters, both radiological and biochemical, before an over-all picture of the progress of a disease can be gained. Another method of measuring bone mineral content utilises the attenuation of a collimated beam of photons passing through, for instance, the radius or ulna; this method does not provide selective information on particular elements. Valuable evidence on skeletal abnormalities can also be gained from the histology of bone biopsy specimens.However, mineral density and biopsy studies may not reflect the state of the skeleton as a whole. On the other hand, a total body measurement is not so sensitive to large changes in a very restricted region of the body.Measurements are repeated at approximately yearly intervals. Developments Two developments in technique that could make neutron activation a more useful procedure are (i) absolute calibration and (ii) partial body activation. With absolute calibration, a single measurement could reveal how far body composition varied from normal. Activation of a restricted region of the body that is known to be particularly affected by a disease could also reduce the dose received by more radiation-sensitive organs.Absolute Calibration Comparison of a phantom of known composition with a patient irradiated and counted under the same conditions is subject to error because of differences in activation and counting efficiencies due to the relative sizes of the patient and phantom and the distribution oi elements within them.We have activated and counted two different sizes of man-like phantom containing equal amounts of sodium nitrate solution. The concentration was uniform through- out each phantom, which consisted of ten polythene containers approximately simulating the various parts of the body. One was of height 170 cm and volume 70 1 and the other was 150 cm tall and of volume 48 1 of the same relative dimensions.Sodium nitrate was used because the sodium-24 produced has a much longer half-life (15 h) than calcium-49 (8.9 min) and emits a y-ray of similar energy (2.75 MeV) to calcium-49. The whole-body counter was calibrated by dissolving the same total activity of sodium-24 uniformly into each phantom.I t was found that the activation efficiency (activity per gram) for the smaller phantom was about 8% higher than for the larger phantom. With regard to distribution of elements, a structure of the approximate geometry of the skeleton consisting of hollow tubes and boxes of Perspex and polythene was placed in the larger phantom. Sodium nitrate solution was activated and counted (i) contained within the mock skeleton and (ii) dissolved uniformly throughout the phantom.Differences in activa- tion and counting efficiences between situations (i) and (ii) amounted to about 2-3%. Total body potassium in patients undergoing activation analysis was measured by oral206 MEDICAL APPLICATIONS OF ACCELERATORS Proc. Analyt. Div. Chem. SOC. administration of about 3 pCi of potassium-42.The potassium-42 provided an internal standard of known activity as it emits a y-ray very similar in energy to that of naturally occurring potassium-40 (1.52 and 1.46 MeV, respectively). Twenty-four hours were allowed for equilibration of the potassium-42 with potassium in the body, a correction being made for excretion. Comparison of patient count rates of potassium-42 and potassium-40 with those from two identical bottles containing a known amount of potassium and the same activity of potassium-42 as was given to the patient allowed us to determine total body potassium in grams.The following linear relationships, applying to both males and females, were obtained by least-squares analysis for each detector geometry : and F = 1.214 + 0.187H - 0.00463M (for LG) .. .. - . (1) F = 1.114 + 0.468H - 0.00762M (for SG) . . . . - - (2) where F is the predicted value of patient 42K count rate per unit activity/bottle 42K count rate per unit activity for a given height (H m) and mass (M kg). Values of F were obtained €or the two sizes of phantom for sodium-24 as well as potassium-42 and it was found that F did not depend significantly on y-ray energy over the range of interest. This fact enabled us to apply equations (1) and (2) to other isotopes.Combination of the correction factors for patient size and element distribution indicates that the absolute amount of calcium in the body can be measured with an accuracy of t 10% with our system. This calibration would be of value in conditions such as osteoporosis where calcium content frequently falls to more than 20% below normal.2 Partial-body Activation In addition to whole-body measurements, we are carrying out activations of one hand of each patient.The hand is placed in a wax “glove” of average wall thickness 6 cm and receives a neutron dose of about 1.5 rad. The beam is collimated to a field size of 21 x 21 cm at the surface of the wax and it is estimated that the whole body receives less than 0.2 reni dose equivalent.The hand is counted by placing it between a pair of detectors, vertically opposed, in the whole-body counter, separated by 8 cm. If it is found that changes in hand calcium correlate well with changes in total calcium, then it may be possible to rely in future simply on a hand measurement. Other parts of the body could be chosen for selective activa- tion but the extremities involve less radiological hazard.Advantage was taken of this activation to determine the rate of loss of sodium-24 from the hand. A series of counts was made up to 48 h after irradiation, beyond which time the sodium-24 activity was barely observable. It was found that the rate of loss of sodium-24 (decay-corrected) could be described by a sum of two exponeiitials : or by a power law: where C is the decay-corrected count rate at t h after irradiation, and A , B, D , x, y and x are positive constants.Equation (4) is a simpler description and furthermore the constants D and x can be obtained with greater precision than the constants in equation (3).Comparing eight patients, suffering from bone diseases, with four people with no skeletal abnormalities, the mean values of x were found to be significantly different. However, the two groups were not very comparable in age or sex and so it is not yet certain whether the procedure will be use- ful diagnostically. No distinction was apparent in terms of the two-exponential analysis.The excellent fit to a power law in all cases suggested that a description involving two compart- ments for sodium (e.g., soft tissue and bone) is an oversimplification. Furthermore, as neutron activation labels all of the sodium equally and simultaneously regardless of compartment, the problems inherent in the use of injected isotopes due to varying exchange rates are avoided... * * (3) . . .. * * (4) C = Ae-zt + Be+ . . .. . . C = Dt-” . . .. .. References 1 . Rewley, D. K., and Parnell, C. J., BY. J . Radiol., 1969, 42, 281. 2 . Cohn, S. H., J . Nucl. Med. Biol., 1974, 1, 131.July, 1976 MEDICAL APPLICATIONS OF ACCELERATORS Feasibility of the Measurement of Whole-body Nitrogen by Collection of Exhaled 11C02 and I1CO 207 B. J. Thomas, M. S. Wright, E.Ozbas” and D. Vartsky Department of Physics, University of Birmingham, P.O. Box 363, Birmingham, B15 2TT The measurement of whole-body nitrogen is of interest because of its proportionality to body protein and hence lean body mass. Thus, a measurement of bodj7 nitrogen content is useful for clinical investigation of a variety of metabolic disorders, e.g., malnutrition, renal failure or cirrhosis.There are two techniques of neutron-activation analysis in current use for the in. vivo determination of whole-body nitrogen. The first employs irradiation with 14-MeV neutrons1,2 and detection of the activity of nitrogen-13 produced in the reaction 14N(n,2n)13N. Nitrogen- 13 decays with the emission of positrons and is identified by the 0.511-MeV annihilation quanta.There are some interferences in the measurement,3-5 perhaps the most difficult being nitrogen- 13 produced by “knock-on” protons in the reaction 16O(p,~)~~N. The second technique6 uses detection of a prompt gamma-ray (E = 10.8 MeV) resulting from thermal neutron capture by nitrogen- 14. The sensitivites of the two techniques are similar, statistical errors of counting being about 2.5% (1 s.d.) for a whole-body dose of approximately 10 mrad.Recently, Palmer7 suggested a new method for measuring body nitrogen by detection of the activity of carbon-11 in the expired air of a subject (as l l C 0 and 11C0,) following irradiation with 14-MeV neutrons. The carbon-11 is produced from a ( p , ~ ) reaction on nitrogen-14 in the body, the protons being hydrogen nuclei “knocked-on” by collisions with the incident fast neutrons. The carbon-1 1 will dissociate from the protein because of recoil and may form 11CO and l1CO,.Collection and coincidence counting of the activity of l l C 0 and l1C0, exhaled in the breath might then provide a measure of body nitrogen. This report considers Palmer’s suggestion in comparison with the other two techniques and presents results from our preliminary investigation of this matter. Method The technique is illustrated in Fig.1. A suitable source of 14-MeV neutrons was not available and hence an alternative cyclotron-produced source was used, namely the reaction of 20-MeV helium-3 particles on carbon. The maximum energy of the neutrons produced was less than the 12C(n,2n) reaction threshold of 18.7 MeV.This source is “wasteful” in an ~ Y Z vivo situation as the low-energy part of the neutron spectrum will not produce “knock-on” protons of sufficient energy to initiate the reaction of interest. I 07 I I Trap 1 Trap2 Trap3 I CaS04 NaOH CuCl inNH40H I CO;! out co out \I ”Fast“ neutrons vCarbon 20-MeV 3He Fig. 1. Illustration of the technique. * Present address : Cekmccc Nuclear Research Centre, PK 1 Havaalani, Istanbul, Turkey.208 MEDICAL APPLICATIONS OF ACCELERATORS Proc.Analyt. Div. Chem. SOC. The gases exhaled by the animal (a rabbit in our studies) were first passed through calcium sulphate in order to remove oxides of nitrogen and water vapour, then through sodium hydroxide solution to absorb l1C0, (and stable CO,) and finally through a solution of copper(I1) chloride in ammonia to absorb T O .The activity of l1C in the traps was measured using coincidence counting of annihilation photons with two 15 x 15 cm NaI(T1) detectors. The half-life was also determined in order to aid in positive identification of carbon-11. Results and Discussion Samples of nitrogen in solution (as ammonium nitrate) were used to investigate the sensitivity of the method and as a test of the chemical separation system.Measurement of the half-life of the activities in each trap indicated little or no contamination of the carbon-11 activity in the sodium hydroxide and copper(I1) chloride - ammonia traps. However, up to 5% of the carbon-11 activity was trapped by the calcium sulphate trap. This problem needs to be investigated in more detail.The sensitivity were 460 counts per kilogram of nitrogen per 0.1 rad from l1C0, and 580 counts per kilogram of nitrogen per 0.1 rad from WO. Both figures are for a count of 5-min duration, commencing 30min after irradiation. These iigures, although encouraging, cannot be used to extrapolate to a count expected in a measure- ment of whole-body nitrogen (approximately 2000 g), because in the in vivo situation an unknown amount of both 11CO and 11C0, will be retained by the body and the remainder exhaled over a relatively long time compared with the half-life of carbon-11 (20.5 min).Palmer showed that T O 2 was expired by a rat with a biological half-life of about 25 min, the corresponding figure for 11CO being about 55 min.The rate of exhalation of the latter was increased by 4.5 times when the animal breathed pure oxygen. We investigated the rates of exhalation of llCO and l1CO, from a rabbit breathing a pure oxygen atmosphere and irradiated with neutrons from the source described. The results of these measurements are summarised in Table I and compared with corresponding results obtained with the rat by Palmer.7 TABLE I SUMMARY OF RESULTS COMPARED WITH THOSE OF PALMER7 Activity Excretion rate produced half -life/ min Experimental in form r--, conditions 11C0/11CO2 For l1C0 For l1C0, Rabbit; pure 0, 2.6:l 17.5 35 Rat; pure 0, 2:1* 127 25* * From Pslmer.7 7 Estimates from Fig.3 in ref. 7. The ratio of the activity of 11C in the two forms, llCO/llCO, = 2.6, is interesting when compared with the result obtained for the aqueous solution of ammonium nitrate (llCO/llCO, = 1.3).This may indicate a biological factor in the formation of l l C 0 and l1CO,, as it is unlikely that a greater fraction of carbon-11 as CO, than CO is retained by the rabbit. Using the counting rates of carbon-11 activity obtained (with the nitrogen content of the rabbit assumed to be 3% of body mass) we estimate that a dose of 0.1 rad of neutrons would be necessary to permit a measurement (with 1 s.d.= 3%) of body nitrogen of a normal adult male. This value compares unfavourably with the sensitivity for the two established tech- niques for which a similar statistical error of counting is obtained with a dose of only 10 mrad. Palmer7 did not give an estimate of the sensitivity from his measurements obtained using the rat.However, the results of our work are appropriate only to the particular neutron source and the sensitivity will be increased by using 14-MeV neutrons. Further work on this subject must involve irradiation with 14-MeV neutrons. The method is attractive because of its relative simplicity but there are many difficulties that need to be investigated.The rate of excretion of l l C 0 and K O , from humans must beJ d y , 1976 MEDICAL APPLICATIONS OF ACCELERATORS 209 investigated and the direct proportionality of carbon-11 activity to nitrogen content needs to be established. The problem of interference from other P+-emitting isotopes of comparable half-life exhaled in the breath must be investigated.In this respect, the efficiency of the chemical removal of nitrogen-13 oxides must be considered References 1. Boddy, K., Holloway, I., and Elliott, A., “In Vim Neutron Activation Analysis, Proceedings of Panel, 2 . Palmer, H. E., and Nelp, W. B., “ I n Vim Neutron Activation Analysis, Proceedings of Panel, Vienna,” 3. Nagai, T., J. Nucl. Med., 1969, 10, 192.4. Cohn, S. H., and Dombrowski, C. S., J. Nucl. Med., 1971, 12, 499. 5. Leach, M.O., MSc. Thesis, University of Birmingham, 1975. 6. Biggin, H. C., Chen, N. S., Ettinger, K. V., Fremlin, J. H., Morgan, W. D., Nowotny, R., and Chamber- lain, M. J ., “Nuclear Activation Techniques in the Life Sciences, Proceedings of Symposium, Bled,” IAEA, Vienna, 1972, p. 49. 7. Palmer, H.E., NASA-CR-141608, Physics and Instrumentation Dept., Battelle, Pacific Northwest Laboratories, Richland, Washington 99352, U.S.A. Vienna,” IAEA, Vienna, 1972, p. 135. IAEA, Vienna, 1972, p. 127. Stable Isotope Tracer Measurements Using Accelerators J. W. McMillan and T. B. Pierce Applied Chemistry Division, A E R E , Har2e~el1, Didcot, Oxfovdshive, OX1 1 ORA The increasing production of the stable isotope tracers hydrogen-2, carbon-13, nitrogen-15 and oxygen-17/oxygen-18 for use in biological and medical sciences is being stimulated by a number of fact0rs.l Firstly, because of their lack of radioactivity, stable isotope tracers can be used in situations where even low-level radioactivity is regarded with concern.Secondly, some ele- men ts, such as nitrogen and oxygen, have only very short-lived radioisotopes, which are useless for most tracer studies.Finally, analytical techniques for the measurement of stable isotope tracers have increased and improved. In reviewing nuclear reaction methods for stable isotope tracer measurements, particularly medical and biological applications using accelerators, their advantages with respect to other methods are emphasised.To this end, four other methods commonly used for stable isotope measurement are outlined with their particular merits. The four methods are infrared spectroscopy, optical emission spectroscopy, mass spectrometry and nuclear magnetic reson- ance spectroscopy. The information they furnish and the type of sample to which they are applicable has been set out by Matwiyoff et aZ.l: Infrared spectroscopy can be used for the determination of the isotope ratios carbon-13 to carbon-12 and nitrogen-15 to nitrogen-14 in simple gases such as carbon dioxide and nitric oxide.Optical emission spectroscopy can be used in a similar manner for isotope ratio measure- ments for simple gases. Mass spectrometry is the most sensitive and precise method for measuring isotope ratios in simple gases, but may also give information on label location in a molecule, and in conjunction with gas chromatography will produce information on complex mixtures.Nuclear magnetic resonance spectroscopy, while not as sensitive as mass spectrometry, can more readily give information on the position of carbon-13, nitrogen-15 and oxygen-17 in a molecule, the measurements being dependent on the non-zero nuclear spin of these isotopes.The method can even be used directly on complex mixtures including whole cell susDensions. These analyrical methods 6roadly achieve two ends. Firstly, some allow the precise measurement of isotope ratios but only in simple molecules usually produced by drastic whole- sale destruction of the labelled specimen, with its inherent problem of dilution with the not unappreciable natural background of the labelling isotopes.Secondly, others permit direct determination of the molecular location of the stable isotope tracer, and in effect the isotope ratio within that molecule.210 MEDICAL APPLICATIONS OF ACCELERATORS Proc. AnaZyt. Div. Chenz. SOC. Although nuclear reaction methods are frequently used for elemental analysis, they involve interaction with specific isotopes and are, therefore, isotopic methods of analysis. Because nuclear reaction methods often require the availability of expensive equipment, such as an accelerator, their use can be justified for stable isotope tracer measurement only if they produce information that is unobtainable by the other four methods, or if they can be made cost effective because of high sample throughputs.Naturally, when isotope sources can be used for certain reactions the cost objections are again avoided. Bearing these factors in mind, possible advantages of nuclear reaction methods are assessed by surveying their applica- tions to stable isotope tracer measurement in biology and medicine. Nuclear Reaction Methods for Stable Isotope Measurements Nuclear reaction methods can be divided broadly into two types, those in which prompt emissions are measured, and those in which a radioactive product is generated and its radio- active decay is measured.In short, they can be termed prompt, and activation or delayed methods. Stable isotope tracers can often be determined by either method.For instance, a prompt method for the determination of oxygen-18is therea~tion~@O(p,a)~~N. Here, the emittedalplia- particles are of a specific energy and can be measured with a particle detector.2 The product nuclide is stable. Amse13 has reported the use of this reaction for the determination of oxygen-18 tracer in rat blood. An alternative delayed method for oxygen-18 is the reaction IsO(p,n)lsF.The reaction has been used for the determination of oxygen-18 in water separated from labelled biological specimens.* Because the composition of the specimen, water, is well defined, the oxygen-18 to oxygen-16 isotopic ratio can be readily deduced from the oxygen-18 content. The method is clearly in competition with the infrared, emission spectrographic and mass spectrometric methods for isotope ratio measurement.However, it is claimed to be as precise and accurate as mass spectrometry and is capable of high rates of sample throughput (as many as 129 per cyclotron run), so making the method reasonably cost effective. An interesting application of the same reaction is the determination of oxygen distributions in urinary calculi from autoradiographs prepared from irradiated ~ections.~ While not aimed at stable isotope tracer measurement, the technique could clearly prove useful to highlight the distribution of stable isotope tracers in sectioned specimens.The oxygen-16 distribution might be determined independently by the reaction 160(3He,p)1sF. Obviously, this type of method will produce similar information to autoradiography using active tracers, even for nitrogen and oxygen elements that have no suitable radioactive tracers.For simple compounds, isotope ratio determination requires only the measurement of the labelling isotope. In complex media, the determination of isotope ratios requires simultaneous or sequential measurement of both isotopes. Isotopic carbon analysis of a variety of tissue specimens including kidney, lung and brain has been achieved by low-energy proton irradiation and measurement of the prompt gamma-rays emitted by the reactions 12C(p,y)13N and 13C(p,y)14N.6,7 The measured isotope ratios were found to have relative errors of between 5 and 10%.While the technique has the desirable advantage of direct application to complex specimens, it will fail to give significant results unless the over-all carbon-13 enrichment of the sample is greater than about 1.3% as opposed to the natural value of 1.1%.This type of re- action method could, however, prove more poweriul if used with a charged particle micro-beam in order to produce information on the spatial location of a stable isotope tracer.8 To date, this application of the nuclear rnicroprobe is still awaited. A further technique for the measurement of the spatial distribution of stable isotope tracers is nuclear track analysis.Carpenter et aL9 have applied the reaction 170(n,a)14C to the determ- ination of oxygen-17 stable isotope tracer in brain tissue. The specimen and an organic film, e.g., cellulose acetobutyrate, in contact, are irradiated with neutrons, and the a-particle induced damage tracks in the film are subsequently developed by chemical etching and are measured microscopically.The density of the tracks can be correlated with concentration. Although accelerators and nuclear reactors are the normal irradiation tools for nuclear re- action methods, simple isotope sources can occasionally be used to good effect.Deuterium can be determined through photoneutron production by irradiation with The ISF is a positron emitter with a half-life of 110 min.July, 1976 MEDICAL APPLICATIONS OF ACCELERATORS 211 gamma-rays having an energy in excess of 2.225 MeV: 2H(y, n)lH. The emitted neutrons are measured with boron trifluoride or helium-3 detectors. Using a 25-Ci sodium-24 (2.75 MeV; t+ = 15 h) source and helium-3 detectors, a sensitivity of 7 counts per minute per microgram of hydrogen-2 has been achieved.1° The method has been applied to whole-body water determination through isotope dilution of injected deuterated water.1° An alternative longer- lived isotope source is thorium-228 (2.62 MeV; t i = 1.91 yr).Greater sensitivity could be obtained by using an electron accelerator produced bremsstrahlung with a maximum energy of 4 MeV.11 I t is interesting to note that both oxygen-17 and carbon-13 should be determinable by photoneutron production.ll An alpha-emitting isotope source, actinium-227, has been employed12 for the determination of oxygen-18 by the reaction 180(cc,n)21Ne. The emitted neutrons were measured with boron trifluoride detectors. Good agreement was obtained between the nuclear reaction method and mass spectrometry for the oxygen-18 content of samples of water and several organic com- pounds. The isotope source was incorporated in an apparatus that largely achieved its inten- tion of providing a simple means of determining oxygen-18 in solid and liquid samples without complex preparation, and appeared to offer the possiblity of future on-line use. Conclusions The most important contribution that nuclear reaction methods can make to stable isotope tracer analysis is in the determination of their distribution in medical and biological specimens. At least three approaches appear feasible : the combination of prompt methods with scanning nuclear microprobes, post-irradiation autoradiography of induced activity and nuclear track analysis. While nuclear reaction methods can be applied directly to the determination of isotope ratios in complex media, the methods often suffer from insensitivity because of bulk dilution by the natural background of the tracer isotope. The application of these methods to separated fractions of specimens or simple degradation products requires special circumstances, for instance a high rate of sample throughput, or the availability of an analytical method based on irradiation with an isotopic source. 1 . 2. 3. 4. 5. 6 . 7. 8. 9. 10. 1 1 . 12. References Matwiyoff, N. A., lieisfeld, M. J . , Mills, T. R., McInteer, B. B., and Goldblatt, &I., “Isotope and Radia- tion Techniques in Soil Physics and Irrigation Studies 1973,” Proceedings of a Symposium, Vienna, October 1973, IAEA, Vienna, 1974, p. 1 1 . .2msel, G., and Samuel, D., Analyt. Chenz., 1967, 39, 1689. Amsel, G., “Proceedings of an International Colloquium on Activation Analysis of Very Low Amounts of Elements, C.E.N., Saclay, October 1972,” Akadkmiai Kiad6, Budapest, 1972, p. 15. Wood, R. A,, Nagy, K. A., MacDonald, N. S., Wakakuwa, S. T., Becliman, R. J., and Kaaz, H., Analyt. McConville, B. E., Proc. SOC. Analyt. Chem., 1974, 11, 123. Ricci, E., Analyt. Chewz., 1971, 43, 1856. Close, U. A., Malanify, J. J., and Umbarger, C. J., Nucl. Iizstvuvn. iweth., 1973, 113, 561. Cookson, J. A, and Legge, G. J. F., Proc. Aizalyt. Div. Chem. SOC., 1975, 12, 225. Carpenter, R. S., Samuel, D., and Wasserman, I., Radiat. Eff., 1973, 19, 59. George, K. D., and Kramer, H. H., Trans. Am. Nucl. SOC., 1968, 11, 474. Bird, J. R., Campbell, B. L., and Price, P. B., Atom. Enevgy Rrv., 1974, 12, 275. Rosenstein, A. W., and Nir, R., Analyt. Claern., 1973, 45, 1707. Chem., 1975, 47, 646.

ISSN:0306-1396    

DOI:10.1039/AD9761300193

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

212 TRACE AMOUNTS OF VOLATILE COMPOUNDS PYOC. Analyt. Div. Chem. SOC. Techniques for the Determination of Trace Amounts of Volatile Compounds The following are summaries of three of the papers presented at a Joint Meeting of the S; L’;L Techniques, Microchemical Methods and Chromatography and Electrophoresis Groups held on February l l t h , 1976. Derivative Spectroscopy R. Staudner Leav Siegler GwzbH, Reuterstrasse 42, 8000 Muvzich 21, West Gevwtavzy Derivative spectroscopy is concerned with the shape characteristics, rather than the basic intensity changes, of a spectral absorption distribution.The slope and curvature charac- teristics are often large, very specific and largely independent of intensity. Because these shape characteristics are large, yet specific to individual compounds, extremely complex separations of component gases are often possible while increasing the sensitivity.Making full use of these advantages, derivative spectrometers (Fig. 1) open the way for both research and practical applications in process control and emission monitoring. On-line control is possible with a quality otherwise attainable only with laboratory instruments, i.e., high specificity and high sensitivity.Sample cell Photomultiplier tube, analysis electronics Fig. 1. inlet - Sample exhaust t A€ Wobbler 0 ____. PIr Wavelength drive programmer -63 Ultraviolet source Diagram of a derivative spectrometer. In the instruments, the radiation emitted by the ultraviolet or visible source is spectrally dispersed by a grating monochromator, providing essentially monochromatic radiation at the exit slit.The wavelength of this monochromatic radiation is varied with respect to time by a laterally oscillating monochromator entrance slit (“wobbler”). Electromechanical displacement of the wobbler is sinusoidal at a frequency of 45 Hz and with a peak-to-peakJuly, 1976 TRACE AMOUNTS OF VOLATILE COMPOUNDS 213 displacement of 0.25-1 mm, depending on the desired amplitude of wavelength modulation.Therefore, the radiation entering the sample cell has a centre value established by the posi- tioning of the grating, but it is also modulated with respect to time. For example, if the amplitude of the wobbler oscillation is k0.5 mm, the wavelength is modulated & 0.15 nm at 45 Hz. Diverging light enters the sample cell from the monochromator and is collected by one mirror located a t the far end of the 1-m cell.This mirror focuses the light at a point on the mirror at the near end of the cell. The light then diverges to the second mirror at the far end of the cell and is, in turn, focused at a new position on the near-end mirror. This process can be repeated as many as 32 times but, in normal operation, light passes through the sample in the cell a total of 12 times (12-m path length). Finally, the light leaves the sample cell and is focused on a photomultiplier tube.The gas sample is drawn through the cell continuously. Alternatively, the pump can be stopped, thus trapping the sample within the PTFE-lined cell. As the second-derivative function is proportional to the amplitude of the second harmonic of the input frequency (45 Hz), the output signal from the photomultiplier tube is electroni- cally analysed for its 90-Hz component.Generally, the amplitude of this component is small in comparison with the total d.c. output voltage and is buried in noise. However, a coil fixed to the wobbler and moving in a magnetic field provides a reference signal having the exact frequency and phase of the wavelength modulation.By electronically doubling the frequency of this reference signal, the instrument locks in on the frequency and phase of the 90-Hz photomultiplier output component. Using these standard phase-lock amplifier techniques, the instrument presents a d.c. voltage representative of the amplitude of the 90-Hz signal component.This d.c. voltage is proportional to the second derivative of intensity with respect to wavelength (curvature). The sample cell contains three spherical mirrors in a “white cell” arrangement. The second derivative of the Beer - Lambert law has four terms, as follows: .. * . (1) .. The first term is a constant, measuring the curvature in the radiation source.The second and third terms may be useful for certain applications but ruin linearity for analytical work. However, by proper choice of wavelength, both terms can be eliminated. For analytical purposes, the wavelength chosen for measurement should be exactly where an absorption band occurs. At this point, curvature will be at a maximum. Also at this point of maximum curvature, the slope is zero.Therefore, the second and third terms reduce to zero at this wavelength and linear measurement with concentration is obtained from the last term. Now, the sensitivity factor is the curvature in absorption coefficient, which discriminates those compounds that create a second-derivative signal. Therefore, equation (1) is reduced to the following: ... . .. . . . . cl/I = -bc d2a - dh2 dX2 The output of the instrument is non-zero only at those wavelengths where curvature is present due to radiation absorption by the sample gases. The output of the instrument is linear with respect to concentration. The complete derivative spectrum for a given gas sample can be analysed for both cornpo- sition and concentration. The individual component gases can be identified by the locations a t which second-derivative peaks occur and the amount of the gas present in the sample can be determined from the height of the peak.Essentially, the instruments have no upper limits to the concentrations that can be mea- sured by proper choice of optical path length provided for by various sample cells. The method provides a direct measurement and analysis of physical properties in real time and without sample conditioning, secondary reactions or sample destruction.214 Proc.Analyt. Div. Chem. SOC. Identification of the Important Contributors to the Aroma of Foods TRACE AMOUNTS OF VOLATILE COMPOUNDS H. E. Nursten Proctev Department of Food and Leather Science, University of Leeds, Leeds, LS2 9JT The perception of odours is still very poorly understood, but it is known that there are about lo7 receptors embedded in the olfactory epithelium compared with about lo5 in the taste buds.Perfumers are said to be able to distinguish about lo4 different qualities, apart from intensities. This has to be compared with the four basic tastes on the one hand and the 7.5 x lo6 colours that the eye is said to be able to discern.The designation of odours is still a considerable problem, but currently one starts with the 44 odour qualities listed by Harper et aZ.l As the olfactory epithelium is situated high up the nose, substances cannot affect it unless they are volatile. Volatile substances are not necessarily odorous and the nose does exhibit a very wide range of sensitivity.The record for the lowest threshold for the human sense of smell is currently held by 2,3,6-trichloroanisole at 3 parts in 10l6 of water.2 Because the constituents of importance as regards aroma may have such low thresholds, they can occur in foods in minute amounts and yet exert a significant organoleptic effect. For 2,3,6-trichloroanisole at 3 parts in 10l6, 3 t of foodstuff would contain 1 ng, which currentlyis about the minimum for identification, and 3 t presupposes 100% efficiency of isolation.It is not surprising, therefore, that Gold and Wilson3 started with 5 t of celery. The total volatile constituents of foods occur in larger amounts, water being by far the most prominent. Ethanol is often present in relatively large amounts and tends to interfere with the process of isolation and identification of the significant volatile compounds.In difficult foods, such as celery, the total volatile compounds constitute about 1 p.p.m., whereas in some types of banana as much as 300 p.p.m. may be present. The mixtures of volatile components of foods are very complex, the number of known constituents increasing as techniques improve.As regards the number of volatile con- stituents identified, coffee has the most with over 500. The significant volatile constituents of fruits and vegetables4 were next considered in turn. Various methods used to obtain such results have been reviewed,5 particularly those developed at Leeds by Cronin and co-workers. Grant's porous-layer open-tubular (PLOT) columns have been modified by replacing the lithium chloride binder by a low-melting Pyrex glass in order to hold the support permanently to the inner circumference of the capillary.Such columns, when coated, have a reasonably high efficiency, yet sufficient capacity for individual components of complex mixtures to be present at a level which permits identi- fication. The columns can readily be re-coated and they are useful in other ways than for gas-chromatographic separation.Short lengths are excellent for trapping gas-chromato- graphic peaks, the traps being sealed immediately and then stored. Subsequently, the contents can be re-chromatographed after breaking the trap in a special heated injection port. Headspace sampling is least likely to produce artefacts, but adsorption of volatile compounds by rubber septa can lead to errors.Because the compounds of interest often have very low vapour pressures, it may be necessary to concentrate the headspace volatile compounds. This concentration can be effected very simply by trapping on very small amounts of charcoal and desorbing the volatile compounds by heating the trap in a special injection port.6 The most widely used method of organoleptic assessment of the volatile compounds from food is to sniff chromatograms at an odour port.In some laboratories the effluent is split and presented simultaneously to several assessors. An alternative is to trap on PLOT Celite capillaries and then to grind these in a small amount of water, presenting the mixture in a vial to a panel of assessor^.^ Trapping on lactose allows incorporation into foods for tasting so that the whole flavour can be assessed, not just the aroma.* The correlation of the analytical and sensory results is one of the most important areas and the two outstanding pieces of work are those undertaken at the Western Regional Laboratoryg and jointly by the groups at SIK, Goteborg, and the Food Research Institute, Norwich.lO Further details of most of the above aspects are readily a~ailable.~Jzdy, 1976 TRACE AMOUNTS OF VOLATILE COMPOUNDS 215 References 1.Harper, R., Land, D. G., Griffiths, N. M., and Bate-Smith, E. C., B Y . J . Psychol., 1968, 59, 231. 2. Curtis, R. F., Dennis, C., Gee, J . M., Gee, M. G., Griffiths, N., Land, D. G., Peel, J . L., and Robinson, 3.Gold, H. J., and Wilson, C. W., J . F d Sci., 1963, 28, 484. 4. Nursten, H. E., Rep. Prog. Appl. Chem. 1971, 1972, 56, 622. 5. Nursten, H. E., I n t . Flavours F d Addit., 1975, 6, 75. 6. Clark, R. J . , and Cronin, D. A., J . Sci. F d Agric., 1975, 36, 1615. 7. Clark, R. J., and Cronin, D. A., J . Sci. F d Agric., 1975, 36, 1009. 8. Yabumoto, K., Jennings, W. G., and Pangborn, R.M., J , Fd Sci., 1975, 40, 105. 9. Guadagni, D. G., Special Publication No. 440, American Society for Testing and Materials, Phila- 10. Von Sydow, E., Andersson, J., Anjou, K., Karlsson, G., Land, D., and Griffiths, N., Lebensm. W i s s . D., Nature, Lond., 1972, 235, 223. delphia, Pa., 1968, p. 36. Technol., 1970, 3, 11. Studies on Flavour-active Sulphur Components of Hops and Beer J.A. Pickett Brewing Research Foundation, Nutfield, Redhill, Surrey, RH1 4HY Many characteristics of beer flavour are derived from olfactory response to necessarily volatile components. Both hops and beer are known to contain a large number of volatile components, many of which have been identified. However, this information has so far been of limited value in providing means for control of beer flavour.Thus, while many relatively maj or volatile components such as 2-methylpropan-1-01 contribute little to beer flavour,2 components present at very low concentrations may affect it markedly. Minor components capable of such action are mostly sulphur-containing compounds.l This paper describes studies on sulphur components of hops and beers that have given rise to practically useful information on hoppy aroma and flavour, and differences between lager and ale.The hoppy aroma and flavour of beer, or hop character as distinct from the hop bitterness, is derived from the essential oil of the hops. However, it is difficult and expensive to impart a consistent and pleasant hop character to beer. Hop oil isolated conventionally by steam distillation at atmospheric pressure is available commercially and may be added to beer but the flavour derived from this product is not satisfactory.Sensory analysis of beers carried out using the flavour profile system developed by Clapperton3 suggested that sulphur compounds contributed to distinction between acceptable hop character and that derived from steam- distilled hop Analysis of hop oil by gas chromatography (GC) coupled with mass spectrometry (MS) using a wall-coated open-tubular column has shown the presence of S-methyl thi~hexanoate.~ However, GC of hop oil using a flame-photometric sulphur detector indicated the presence of many more sulphur compounds, but only S-methyl thiohexanoate could be identified by GC - MS using the open-tubular column.An alternative approach was devised, which involved GC - MS using packed columns. This technique allowed a greater sample size, but required knowledge of the exact points at which the sulphur compounds occurred in the chromatogram obtained from the total ion current monitor. This information was obtained by using a Pye GCV chromatograph, which allowed simultaneous detection by flame ionisation and flame photometry.Chromatograms obtained in this way are shown in Fig. 1. The sulphur compounds are at such low levels that they give little response with the flame-ionisation detector and are in fact not coincident with any distinct peaks recorded by this means. However, the exact points of elution of sulphur compounds relative to peaks in the flame-ionisation chromatogram were determined and the time lag between flame ionisation and total ion current response was measured.Mass spectra were then obtained for the regions in which the sulphur compounds were eluted. Mass- spectral features that reached maxima at the exact points at which the sulphur compounds were calculated to enter the source of the mass spectrometer were isolated from the other data.To facilitate these studies, narrow fractions of hop oil, taken from the regions in which sulphur compounds were known to be eluted on preparative GC using analytical columns, were employed. The mass-spectral information thus obtained was used to provide tentative identification of the sulphur compounds. Flavour thresholds for beer components may differ1 by a factor of 2 x 10l2.216 TRACE AMOUNTS OF VOLATILE COMPOUNDS Proc.Analyt. Div. Chem. SOC. 60 40 20 0 Time/min Fig. 1. Gas chromatograms of hop oil obtained by using (a), a synchro- nised flame-ionisation detector and ( b ) , a flame-photometric detector. For identification of peaks see text. Peak D in Fig. 1 was shown, by peak-enhancement studies with the authentic compound, to arise from S-methyl thiohexanoate.Mass-spectral features for this compound were observed at the point at which the compound was calculated to enter the mass spectrometer. However, while GC - MS of the pure compound gave a parent ion with an intensity of 2y0 of that of the base peak (m/e 43), no parent ion was seen when the fraction of hop oil was analysed. When the pure compound was analysed by GC - MS using a field ionisation source, a parent ion with an intensity of 21% of that of the base peak (m/e 99) was found.However, GC - MS of the hop oil fraction again showed no parent ion. Subsequent work was therefore carried out by using the simpler electron impact system. The techniques described here were used to identify tentatively peaks A, B and C as arising from isomers of S-met h yl t hiobut yrat e, t hiopen t anoat e and t hiohexanoat e, respectively .Peak E possibly arose from a sesquiterpene episulphide. By synthesis of authentic com- pounds, and peak-enhancement studies using different chromatographic systems, peaks B and C were shown to arise from S-methyl thio-2-methylbutyrate and S-methyl thio-4-methyl- pentanoate, respectively.Thioesters identified as components of conventional steam-distilled hop oil were obtained chromatographically pure and added to beer, separately and in admixture, at the concentra- tions attained when conventional steam-distilled hop oil is added to beer. High scores for flavour profile terms associated with unsatisfactory hop character were ~btained.~ It was therefore considered desirable to produce a hop oil containing much lower levels of sulphur components.A new process for isolation of hop oil was developed and the product did indeed give rise to a satisfactory hop ~haracter.~ Sulphur-containing compounds were considered likely to contribute to differences between lagers and ales. That dimethyl sulphide can contribute to lager flavour has been established previously.6 However, it was necessary to identify other sulphur-containing components in- volved in differentiation between lager and ale flavours.New procedures were required for obtaining concentrates of the volatile components of beer and this aspect of the study was initially more important than GC and GC - MS techniques. The isolate was then fractionated by distillation under vacuum7 between four traps, one held at Relatively highly volatile components were isolated from beer by vacuum stripping.July, 1976 IMMOBILISED ENZYMES AS CATALYSTS 217 -46 "C, two at -116 "C and one a t -196 "C.The traps held at -116 "C contained minor volatile components, which were transferred under vacuum to a tapped ampoule fitted with a rubber septum.A series of lagers and ales were extracted by this means and a number of differences in levels of sulphur components between these types of beers were observed in addition to those for dimethyl sulphide, e.g., the ales contained more dimethyl disulphide while the lagers contained more ethyl methyl sulphide.2 Extracts from beers to which known amounts of the sulphur compounds under investigation had been added were then obtained.GC analysis of the ex- tracts showed that the differences in concentrations of the compounds were generally much lower than their respective flavour threshold values. The quantitative studies also demon- strated that sulphur compounds a t levels well below 1 p.p.b. could be detected by using the extraction procedure.Beer components with lower volatility were isolated from beers by steam distillation at low temperature. The distillates were then extracted with highly purified diethyl ether, which was removed under vacuum to yield concentrates that were stored in evacuated all-glass ampoules.7 Concentrates from a series of lagers and ales were obtained and analysis showed that ales contained more of certain heterocyclic compounds.2 However, although sulphur atoms were present in some of the compounds found at higher levels in ales, e.g., 2-acetylthiophene, other compounds without sulphur, e.g., 2-acetylfuran, were also involved. The study of volatile components of lagers and ales so far suggests the absence of any major contribution to lager character from sulphur compounds other than dimethyl sulphide. The author thanks Professor J. A. Elvidge for provision of facilities for GC - MS studies by electron impact and Dr. D. E. Games for carrying out GC - MS by field ionisation. References 1. Meilgaard, M. C., Tech. Q. M.B.,4.A., 1975, 12, 151. 2 . Pickett, J. A., Coates, J., Peppard, T. I>., and Sharpe, F. K., J. Inst. Brew., in the press. 3. Clapperton, J . F., J. Inst. Brew., 1974, 80, 164. 4 . Pickett, J . A., Coates, J., and Sharpe, F. R., "Proceedings of theEuropean Brewery Convention Con- 5. Buttery, R. G., Black, D. R., Guadagni, D. G., and Kealy, hf. P., PYOC. A m . SOC. Brew. Chew., 1965, 6. Anderson, R. J., Clapperton, J. F., Crabb, D., and Hudson, J . R., J . Inst. Brew., 1974, 79, 495. 7. Pickett, J . A., Coates, J . , and Sharpe, F. K., J. Inst. Bvew., in the press. gress, Nice," Elsevier, Amsterdam, 1975, p. 123. 103.

ISSN:0306-1396    

DOI:10.1039/AD9761300212

出版商:RSC    

年代:1976

数据来源: RSC

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July, 1976 IMMOBILISED ENZYMES AS CATALYSTS 217 Immobilised Enzymes as Catalysts The following is a summary of a paper presented at a Joint Meeting of the Midlands Region and the Loughborough University of Technology Chemical Society held on March 2nd, 1976. lmmobilised Enzymes as Industrial Catalysts for Production and Analysis S. A. Barker Departwent of Chemistvy, Univevsity of Bivminghanz, P.O.Box 363, Edgbaston, Bivmingham, B15 2TT Immobilised enzymes are now attractive tools for analysis in a variety of forms such as tubes, fibres or porous supports. Their uses in the form of membranes have not been fully exploited. It is now feasible to immobilise an enzyme in situ on one side of a conventional dialysis membrane set up as the dialyser unit of an AutoAnalyzer and then to proceed, without dis- mantling, to use that membrane for the analysis of one component of a flowing mixture of naturally occurring macromolecules such as nucleic acids, proteins or polysaccharides.The enzymes so used can often be commercially available hydrolases so that a specific product of small relative molecular mass diffuses through the membrane and is assayed in the con- ventional way.218 0 R IT U A RY Proc.A$zalyt. Div. Chem. SOC. This type of approach can be extended to the specific analysis of small metabolites by using acrylic acid grafted dialysis membranes to retain sugar phosphates and inorganic phos- phate on one side of the membrane while permitting the rapid diffusion of the parent sugars. In this laboratory Rattle has recently designed a multi-stage enzyme-membrane reactor to effect the conversion of glycogen or starch to fructose, using four enzymes: (1) phosphorylase, in the presence of phosphate, to convert these polymers to glucose-1-phosphate, (2) phos- phoglucomutase, to catalyse the conversion of glucose-1 -phosphate to glucose-6-phosphate, which then becomes the substrate of (3) phosphoglucose isomerase, to give fructose-6-phos- phate, which is broken down by (4) alkaline phosphatase, to fructose.Solving this sort of problem effectively demonstrates the versatility of modern enzyme immobilisation procedures in their ability to ( a ) change the pH optimum of an enzyme on immobilisation so that it is compatible with another immobilised enzyme, ( b ) enhance the heat stability of the enzyme so that a half-life of a minimum of 200 h can be assured and (c) act with high efficiency on their substrates.A special problem arises under (c) in the instance of very large substrates such as glycogen/starch, as many immobilisation procedures, parti- cularly those based on entrapment, are ineffective. The porous nature of the support, the size of the pores and a surface coating of enzyme are the vital parameters that should be examined in order to solve this problem. Automated analysis without the continuous use of expensive consumable reagents appears to be an analyst’s dream but is accessible in the world of the sensor such as an enzyme electrode.An oxygen electrode for sensing oxygen consumption in combination with immobilised glucose oxidase permits rapid, accurate assay of glucose in serum samples.Eagling, in this laboratory, has extended this concept to the “sensing” of starch and sucrose by immobilising glucoamy- lase and invertase, respectively, in combination with the glucose oxidase. Surprisingly good response times are retained in going from the one-enzyme to the two-enzyme electrode.Enzyme discs stable for 1-2 years have been prepared yet instrument manufacturers are loathe to enter this uncharted field. Finally, near perfection has been achieved by several industrial companies in producing immobilised glucose isomerase packings able to operate on 50% m/wz glucose solutions with residence times of 1-2 h at 60-65 “C to produce the requisite 42% conversion to fructose that makes the product as sweet as sugar. A minimum half-life of 500 h can be virtually guaran- teed provided the quality of the glucose feed is high, particularly in the absence of calcium(I1) ions. The UK will shortly have this product, alas based on imported maize rather than starch derived from home-grown wheat, which would provide gluten as a by-product to enable us to solve another problem, to make bread with our own low-gluten wheat. Here is an area where Government help would be welcome in organising a scheme that could be a replica of that operating with sugar beet growers.

ISSN:0306-1396    

DOI:10.1039/AD9761300217

出版商:RSC    

年代:1976

数据来源: RSC

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218 0 R IT U A RY Proc. A$zalyt. Div. Chem. SOC. 0 bituary James Bernard Attrill James Bernard Attrill, who was for nearly 20 years Editor of The Analyst, died on May loth, 1976, after a short illness; he was 52 years of age. He received his early education in Beckenham and later in Bath, from where he entered St. John’s College, Cambridge. His studies were, however, interrupted by the Second World War and before returning to Cambridge, where he obtained his BA degree in 1949 and was awarded his MA in 1951, he had experienced employment in the electronics industry, on the production of early radar equipment, and in book production with Edward Arnold & Sons, the medical publishers.He was elected a Fellow of the Royal Institute of Chemistry in 1954. After a brief period with the Iron and Steel Institute Jimmy Attrill joined the staff of The Analyst in February 1950 as Assistant Editor, and in January 1954 he was appointed Editor in succession to the late F.L. Okell. He was the eighth Editor of the journal and the first who had not primarily been a practising analyst. His Editorship of The Analyst, which ended when he assumed responsibility for the pro- duction of analytical books and monographs in August 1973, covered a period of change andJuly, 1976 EQUIPMENT NEWS 219 growth.It began with a change in both the name and the image of the Society and with an increase in the size of the journal brought about by the ending of the war-time paper restrictions. Attrill’s keen knowledge of typography and lay- out ensured that the image of the journal kept pace with that of the Society, and his scrupulous attention to accuracy and detail was reflected not only in The Analyst, but also in PvoceediNgs of the Society f o v Analytical Claevtzistvy and in the various books and series of monographs that were begun or published under his Editorship. This same desire for accuracy and his interest in typography were evident when he took over all analytical book production; he has set a high standard that will not be easily maintained.Those who met Attrill will remember him as a friendly person ; many who did not meet him will remember the friendly manner in which he conducted negotiations either by letter or tele- phone, and some authors of papers for publica- tion that were rejected by The Analyst later had cause to thank him for his advice and encouragement.He was a man with few interests outside of his work, although he did have a considerable affection for British postage stamps, his one regret being that he was never in the right Post Office when a defective sheet of a new issue was offered for sale. The history of the Society for Analytical Chemistry and the history of railways in this country were other interests of his on which he would speak auth- oritatively. For more than 25 years Jimmy Attrill loyally served the Society for Analytical Chemistry and more lately The Chemical Society ; he will surely be missed. He is survived by his wife Patricia and by his two sons Peter and William. Peter W. Shallis

ISSN:0306-1396    

DOI:10.1039/AD9761300218

出版商:RSC    

年代:1976

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July, 1976 EQUIPMENT NEWS 219 Equipment News Measurement of Binary Gas Mixtures The 7 5 TC is a portable instrument for measuring a wide variety of binary and some ternary gas mixtures, such as helium, hydrogen or carbon dioxide in air, methane in nitrogen, and natural gas in town gas. It is battery operatecl and uses a thermal conductivity detector. Crowcon (Instruments) Ltd., Shelley Close, Headington, Oxford.Gas Monitors A modular gas-monitoring system is announced, on which all the adjustment and calibration controls, despite being accessible from the fascia, are protected from interference by unauthorised personnel. The DI 230, which is mainly for use in the oil, gas and petrochemical industries, pro- vides fully automatic detection of combustible gases and the necessary control action.The instruments are electro-catalytic in principle and give a direct reading of combustible atmospheres. An element that is insensitive to the gas compensates for changes in tempera- ture, pressure and humidity. Detection Instruments Ltd., 3 Rectory Road, Wokingham, Berks., R G l l ID J . Interval Timer The modular digital interval timer has a number of advantages over the conventional stopwatch, e.g., elimination of reading errors, timing to within 0.1 s of periods up to 28 h and a continu- ous acciiracy of O.Olyo. T t is mains operated but the frequency of the quartz-crystal oscillator is independent of mains frequency and is con- trolled to within &O.Olyo a t ambient tempera- tures between 18 and 22 "C.One clock module can be used to drive up to five separate electro- mechanical counter units.I t operates a t 100 kHz and the output is divided by 10 000 in a series of TTI, logic circuits to give one pulse every 0.1 s. Incorporated in each counter unit is a &digit display, to give a timing maximum of 99 999.9 s. Townson & Mercer Ltd., Beddington Lane, Croydon, CR9 4EG. Microscopy The Hitachi - Perkin-Elmer Model H500 is claimed to provide the greatest degree of versa- tility combined with specimen preservation yet attained in any transmission electron micro- scope. The advantages of both top- and side- entry stages are available without any major modifications to the objective lens.The evalua- tion of specimens down to 0.1-0.4 nm resolution over a magnification range of lOOx to 8 x lo5 x is pxsible and contrast levels 12 times those obtained by conventional microscopy can be achieved.Many other features and accessories are available, such as push-button selection of operating modes, a fully automatic fail-safe re- cycle vacuum system, X-ray energy analysis and scanning accessories. Analysis of frozen sec- tions of biological material is possible by the220 EQUIPMENT NEWS Proc.Analyt. Div. Chem. SOC. combined use of the side-entry cold stage with the scanning accessory and X-ray spectrometer. Perkin-Elmer Electron Microscopy News 8 in- cludes an article on electron microscopes. Perkin-Elmer Ltd., Post Office Lane, Beacons- field, Bucks., Hp9 1QA The Technival stereomicroscope supersedes the SMXX. With the standard objective the magnification range is from 6 .3 ~ to lOOx but with supplementary lenses this can be extended from 3 . 2 ~ to 200x. Illumination can be adapted to the samples and double binocular viewing tubes are available. Photographs of specimens can be taken, measuring and counting facilities are provided by suitable eyepieces and polarisation can be used. Drawing attachments are also available.Carl Zeiss Jena Ltd., 2 Elstree Way, Boreham- wood, Herts., WD6 1NH. Analysis for Carbon and Sulphur The NP8 Induction Furnace and ER CS Analyser are for the determination of carbon and sulphur in a wide variety of products such as metals, cements, petroleum products and glasses. Amounts of these elements in the range from a few parts per million up to 80% can be determined.Garrick Equipment Co. Ltd., 13 Garrick Street, London, WC2E 9AR. Signal Conditioner An eight-channel signal conditioner is available for use with analytical equipment that has low- level d.c. voltage output signals. Although intended primarily as an extension to the Venture A8 Data Loggers, this conditioner is suitable for most analytical-processing systems.Features include high impedance, differential mode operation accommodating inputs from 8 mV to 1 V f.s.d. in 4 ranges, an output range of 0-1 V f.s.d., independent channel controls pro- viding gain control over each range and offset adjustment of &200%. Smiths Industries Ltd., Industrial Instrument Division, Waterloo Road, Cricklewood, London, NW2 7UK. Analysis of Water An expanded low-range accessory that fits all current Hach Series DR/2 spectrophotometers is available.It consists of a sample cell cham- ber with a 10-in sample cell and a photocell holder cap assembly. The light beam is directed through the bottom of this cell and projected upwards to the photocell. This pro- vides a light path ten times longer than t h a t through the standard horizontal sample cell.With this accessory constituents in water a t the microgram per litre level can be measured. Hach Chemical Co., P.O. Box 907, Ames, Iowa 50010, USA. Spectrophotometry A new ultraviolet - visible spectrophotometer is announced. The Model 550 is a double-beam instrument fitted with a grating monochromator and automatic stray-light filters. With the ultraviolet attachment an automatic light-source change operates a t 315 nm.This feature, to- gether with automatic filter change and scan stop a t the end of the range, offers a facility previously confined to more expensive instru- ments. There is automatic push-button setting of zero absorbance and a large sample compart- ment with optional automatic sampling. Pre- sentation of results is on a digital printer and an accessory is available that permits first or second derivative absorbance spectra to be recorded directly.Also available is the Model 200, which offers a wide range of facilities in the ultraviolet and visible regions, and the Model 575 for measurements in the ultraviolet region. Perkin-Elmer Ltd., Post Office Lane, Beacons- field, Bucks., HP9 1QA. A microcomputer-controlled infrared spectro- meter which is claimed to represent a significant advance in automated multi-component analy- sis of liquids and gases is announced.The Model 80 combines the features of the Miran infrared analyser with the Intel 8080 micro- processor and enables up to 16 separate wave- lengths to be measured in less than 2 min, generally without prior sample preparation.The instrument is suitable for repetitive analyses in the laboratory and the continuous analysis of process streams. Wilks Scientific Corporation, P.O. Box 449, S. Norwalk, Connecticut 06856, TJSA. Filters for Gases and Liquids A T-type design of in-line filters, which features removable elements while the housing is in-line, is available. The filters in the Nupro range are all-metal and are suitable for temperatures up to 600 O F (stainless steel) and 300 O F (brass models).They can also be used a t pressures as high as 6 000 and 2 000 p.s.i.g., respectively. Housings are in 316 stainless steel or brass with sintered and wire mesh elements in stainless steel covering the size range 2-440 rum. L4pplications include sampling systems, protection of sensitiveJuly, 1976 CONFERENCES AND MEETINGS gauges and analytical and control instruments.Midclx., HAS SJP. Techmation Ltd., 58 Edgware Way, Edgware, NMR Spectrometry The WP-SO/DS pulsed Fourier Transform NMR Spectrometer is a low-cost fully multi-nuclear instrument operating a t 18.8 kG, corresponding to 80MHz for IH. Interchangeable probe- heads and plug-in transmitter - receiver units are uscd to facilitate changeover of nuclei. A programmable data-processing computer equipped with all interfaces necessary for highly automated operation is incorporated. There are many other features such as aregister - display unit for user programming, a switchable format digital X - Y plotter, a display oscilloscope, and a 2H heteronuclear lock unit with automatic Y-gradicnt control and lock level monitor. Also available are a number of optional access- ories. Bruker Spectrospin Ltd., Unit 3, 209 Torring- ton Avenue, Coventry, CV4 9HN. 22 1

ISSN:0306-1396    

DOI:10.1039/AD9761300219

出版商:RSC    

年代:1976

数据来源: RSC

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July, 1976 Conferences and CONFERENCES AND MEETINGS 22 1 Meetings Micro 76 International Symposia and Exhibition SPptembev 13-16, 1976, Lovldon Micro 76, an international conference on microscopy, together with an international exhibition of modern microscopes and ancillary equipment, is being organised by The Royal Microscopical Society and will be held a t the Bloomsbury Centre Hotel, Coram Street.London, W.C. 1. Symposium sessions include light and electron microscopy in both life and materials sciences. Further information is available from the Administrator, Royal Microscopical Society, 37/38 St. Clements, Oxford, OX4 1AJ. Fifth Thermal Analysis School September 13-17, 1976, Salford the First European Symposium on Thermal Analjrsis. The School is designed to give scientists and technologists a general introduction to the theory and practice of thermal analysis, which will enable them to evaluate critically the uses of these techniques in relation to their own analytical testing or research requirements. Further information from The Administra- tive Assistant (Short Courses), Room 2, Univer- sity of Salford, Salforcl, M5 4WT.First European Symposium on Thermal Analysis Septembev 20-24, 1976, Salfovd This Symposium is organised by the Thermal Methods Group of the Analytical Division of The Chemical Society and will be held a t the University of Salford.All aspects of thermal analysis will be covered, including instrumentation and techniques, aspects of physical, organic and polymer chemistry and the application of thermal methods in applied sciences such as mineralogy, corrosion, pharmaceuticais, ceramics, building materials and glass technology.There will be three plenary lectures : “Com- bined Techniques,” by Dr. F. Paulik (Technical LJnivcrsity, Budapest) ; “Reaction Kinetics,” by Dr. J. Zsako (Rumania); and “Thermo- metric and Enthalpimetric Titrimetry,” by Dr. I,. S. Bark (University of Salford).Approxi- mately 100 papers have been accepted for 7 sessions and there will also be informal discuss- ions. Registration forms should be returned by August 23, 1976. Further details from The Administrative Assistant, First European Sym- posium on Thermal Analysis, Room 2, IJniversity of Salford, Salford, h15 4WT. Fourteenth Conference on Vacuum Micro- balance Techniques Septeivlbev 27-28, 1976, Salfovd This Conference will be held a t the University o f Salford and papers will be presented on theoretical and experimental work involving The Thermal Methods Group of the Analytical microbalarice techniques. Division of The Chemical Society will be Further information from The A4dministrative holding the Fifth Thermal Analysis School a t the Assistant (Short Courses), Room 2, University I’niversity of Salford during the week preceding of Salford, Salford, &I5 4WT.

ISSN:0306-1396    

DOI:10.1039/AD9761300221

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

222 COURSES Publications Received Dimethyl Sulphoxide. D. Martin and H. G. Hauthal. 'l'ranslatxl by E. S. Halberstadt. Pp. xviii -1- 600. TVokiiig- ham: Van Nostrand Keinhold. 19';J Priic ,@o. Understanding and Optimising EPe~troa Microscope Performance, S. K. Chapman. Pp. iv + 92. Rcnconsfield, Buckinghamshire : Perkin-Elmer EM Pxblica- tions. Z D i 6 The Hydrolysis of Cations. Charles F.Baes, J r . , and Robert E. Mesmer. Pp. xxii + 489. New York, London, Sydney and Toronto: John Wiley. 1976. L18.60; $33.25. Emission Spectroscopy. Edited by Ramon M. Barnes. Pp. xii + 548. Stroudsburg, Pa. : Dowden, Hutchinson and Ross. Distributed by Halsted Press. 1976. Price A21.75; $38.85. Wilson & Wilson's Comprehensive Analyti . cal Chemistry, Volume VII. Tkermsl Methods in Analytical Chemistry.SuS - stoichiometric Analytical Methods. Edited by G. Svehla. Pp. xvi + 322. Amster- dam, Oxford and New York: Elsevier. 195:; Price Df1125; $49.95. The Physical Basis for Heterogeneous Catalysis. Edited by Edmund Drauglis and Rolmt I. Jafiee. Pvoceedimgs of the Ninth Battell.;. Col- loquium in the iwatevials Sciences, Gst-inJ, Switzevland, September 2-6, 1974. Pp. xxvi 4- 596. New York and London: Plenum. 1975. Price $54. Ion- Exchange Chromatography. Edited by Harold I;. Walton. Benclminrk Papevs in Analytical Clzemistvyll. Pp. xx -1 440. Stroudsburg, Pa. : Dowden, Hutchinson & Ross. Distributed by Halsted Pres. 1976. Price L18.65; $33.30. Printed by Heffers Printers Ltd Cambridge England

ISSN:0306-1396    

DOI:10.1039/AD976130222b

出版商:RSC    

年代:1976

数据来源: RSC